Sam Wallace: Mystery of the missing midfields...

What happened to the rest? Nine points separate the reigning champions from the trailing pack as we approach the halfway point this week: the kind of lead that has not been seen at this stage in the Premiership since Newcastle went 10 points clear at the mid-point of the 1995-1996 season before throwing it all away. English football awaits what we now know as the "blip", only for Chelsea the blip seems to last no longer than just that - a heartbeat, a half of a match, a momentary loss of concentration. They seem immune to a sustained collapse.

This season, Frank Lampard and Michael Essien have come to represent all that is strong about Chelsea as well as emphasising the key elements that Manchester United, and Arsenal, lack. A swift and devastating change in the hierarchy of English football has taken place within the space of five months with the departure of both Roy Keane and Patrick Vieira, and they have left behind problems that could endure for years. Replacing a goalscorer, a goalkeeper or a defender looks like a relatively easy task compared to finding a player who can set the mood, tempo and character of a team.

It is tempting to look at the progress Chelsea have made and identify two moments as definitive even before Roman Abramovich's fortune made bidding against them in the transfer market financial suicide. In the summer of 2001, United bought Juan Sebastian Veron for ?27m while Chelsea invested less than half that with the ?11m purchase of Lampard. Two years later, and offloading Veron for ?15m to an Abramovich regime that would pay any price, United spent ?9.4m on Kleberson and Eric Djemba-Djemba while in France, Essien quietly moved from Bastia to Lyon.

There is nothing revelatory about the theory that Keane and Vieira represented something at their clubs that would be difficult to replace, it was just that when they were finally allowed to leave it seemed inconceivable that there would be no plan in place to replace them. In both their departures, there was the sense that - for very different reasons - their clubs had been forced into the decision, rather than any reassurance that both United and Arsenal had resolved they could get along quite nicely without them.

Chelsea are not football aesthetes in the manner of Arsène Wenger's 2004 champions, or the United side that dominated at the start of the decade, but they do, however, know who they are and what they represent. They are a team built in their manager's image, who are driven on by Lampard and John Terry in a system that never changes. United have already abandoned the 4-5-1 formation this season and have a converted striker in Keane's old role. Arsenal have had to rely upon the 18-year-old Cesc Fabregas and the anonymous Mathieu Flamini to take on Vieira's job.

United may have beaten them once, and Arsenal have qualities that Jose Mourinho's side will never match, but neither have come close to sustaining the momentum that has carried Chelsea this season. They were just five points clear at the halfway point last year and then embarked upon a run in the second half of the season that began with seven straight victories before Manchester City finally managed to slow them with a draw on 6 February. Spotting where - or who - might slow them down is becoming an ever more hopeless task.

From the middle of January for what could be up to one month, Mourinho will have to compensate for the loss of Essien and Didier Drogba, who will be at the African Nations Cup in Egypt. Their importance to the grand Chelsea project, to making work the formation that Mourinho prefers to play, cannot be understated and in a squad he has trimmed to 23 their absence will be felt. But their time away coincides with a run of fixtures that has been kind to Chelsea: Sunderland, Aston Villa and Middlesbrough away, Charlton and Liverpool at home.

In fact, the only fixture that casts a shadow over Chelsea's progress is their Champions' League tie with Barcelona, possibly the only team in Europe with the capacity to provoke genuine uncertainty in them. The Spanish champions are beginning to feel like the last chance to throw tacks under Chelsea's wheels and only they - Ronaldinho and Samuel Eto'o in particular - seem capable of inflicting the kind of defeat that might give Mourinho's team a wider cause for self-doubt. Should Chelsea secure the stupendous achievement of eliminating Barcelona twice in two years then nothing will seem impossible to them.

When the Champions' League begins again at the end of February, Manchester United might be glad of the midweek rest but precious little else. For them, a second half of the season without the interest of European football is like a movie without the soundtrack: the action rolls on but there is little help making sense of it. Over more than a decade, supremacy in the Premiership, or close to that, has been comfortably within United's grasp and the Champions' League has been where Sir Alex Ferguson's team have gone to define their true status. Denied that challenge now, their world seems to have shrunk a little, their capacity to improve reduced.

Ferguson will not have any discussion of the club's life beyond this summer, or how much his future is affected by individual results - it is a topic off limits with even those who still enjoy his favour. His theory seems simple enough: that by permitting one fissure in the rock of his authority he risks the disintegration of it all. Cutting loose Keane was a way of telling his players that, however long the current administration lasts, it will not leave any of the tough decisions that can be made now for its successors to bear.

It has become a familiar question in the analysis of United's season, but how can a team in second place in the Premiership so often be involved in matches that would seem to define their season? Chelsea on 6 November, Benfica on 7 December, Everton four days later and even Wigan four days after that have all come laden with doom. Defeat in Europe has removed the margin for error at Old Trafford, there is no Plan B if their campaign in the Premiership fails. Yet with a total of 37 points after 17 games their record bears comparison with recent seasons.

Last season they were fourth with 37 points at the halfway point of 19 games and only twice since 2000 have they had more than 40 points at that stage of the season. The last time United won the title, in 2003, they began the second half of the campaign with only 35 points, but now it all appears little use in the face of a Chelsea team who amassed 49 points in the second half of last season, especially when the chasing pack capable of placing pressure upon Chelsea seems to have dwindled so badly of late.

Defeat to Chelsea at Highbury was the beginning of Arsenal's long farewell to their title challenge and after 16 games this season, they have eight fewer points than at the same stage last year. They faced Lampard, Essien and Claude Makelele without the suspended Gilberto Silva and only Fabregas and Flamini to defend what was left of the Arsenal midfield. At 18, the Spanish midfielder has a great deal to look forward to in his career, but even before you consider that Flamini is being asked to replace Vieira it is hard to imagine the younger Frenchman making any of the three title-winning sides Wenger has built.

In Arsenal's malaise there are echoes of United's problems - both clubs seem to be bracing themselves for the decisions that will have to be made by key individuals at the end of the season. For United that question concerns Ferguson and for Arsenal it means Thierry Henry, with one year left on his existing deal, who must either sign a new contract or be sold in the summer. At a club still absorbed with the question of replacing Vieira it seems like the cruellest of tasks.

That same uncertainty that followed Liverpool and Steven Gerrard for more than a year has been dealt with by Rafael Benitez, whose side returned from Japan this week with only 15 games played and a lot of catching up to do. With 31 points they have eight more than at the equivalent stage last season when they climbed to seventh after beating Arsenal with Neil Mellor's goal at Anfield. Benitez has transformed a defence that is no different in personnel to last season into the second best back four in the Premiership behind Chelsea's.

Tottenham are nine points better off after 17 games than they were at the same stage last season and they can still afford to keep Jermain Defoe on the bench. At a club who have at least six Englishmen who can count themselves as a safe bet to start matches, Defoe has not made the first XI for the last four games - the surest sign of the strength within Martin Jol's squad. Edgar Davids will be 33 in March and yet already he looks like one of the best acquisitions of the summer.

The three English managers in charge of the Premiership's emergent clubs - Sam Allardyce, Paul Jewell, and Stuart Pearce - have all transformed their teams over the last 12 months but it is indicative of the state of their profession that only the Bolton manager will really be seriously considered when Sven Goran Eriksson's successor is chosen next summer. After promotion in 2001, Allardyce has forced his club's progress beyond the annual fight against relegation - in the English managers' league within the Premiership, the case he is making to the Football Association is becoming harder to ignore.

Wigan could be safe from relegation by the end of January, which is only one way of conveying the scale of Jewell's achievement, while Manchester City's Pearce and West Ham's Alan Pardew have also given more weight to the renaissance of the English manager. Unlike their foreign counterparts, we have witnessed every stage of their careers - Jewell's relegation with Bradford, Pearce's brief time in charge of Nottingham Forest and Pardew's struggles to tame West Ham's vast expectations. English managers are not - unlike Mourinho, Benitez and Jol - delivered to us with their mistakes made out of sight in distant, unknown leagues and their reputations can suffer accordingly.

The Premiership now has 16 British and Irish managers and they range from those who will see the next few months as a simple case of avoiding relegation to Mick McCarthy, whose Sunderland team have five points after 17 games and, surely doomed already, are close to an unwelcome record. They could face the halfway stage with fewer points than any other side in Premiership history - a distinction currently held by Sheffield Wednesday who had six at the same stage of the 1999-2000 season.

Last season, Chelsea were the first team since 2000-2001 to lead the Premiership at its halfway stage and hold on to win in May and then, even with 46 points at the turn last Christmas, there seemed a degree of uncertainty about whether they could sustain the pace. Now those questions focus more on Chelsea's pursuers and whether they can keep within a respectable distance of the Premiership champions should they finally encounter something - or some opponent - capable of nudging them from their stride.

So Far So Good (or bad) Sam Wallace's half-term awards...

* FOR THE BEST GOAL SO FAR

Portsmouth's Matthew Taylor had already scored once against Sunderland on 29 October when, 45 yards from Kelvin Davis' goal, he struck a perfect dipping volley into the net. For Alain Perrin it was a definite high point: he never won another game in charge of Portsmouth and was sacked less than a month later.

* FOR COMING GOOD AT LAST

When Robin van Persie was picked ahead of Dennis Bergkamp to start against Chelsea eight days ago he must have known he had arrived at last. He seems to have conquered his temperament now - his goal against Blackburn on 29 November was a masterpiece - and come next season he may have to replace not one but two famous Arsenal strikers.

* FOR CONTINUED EXCELLENCE

At 31, with a Euro 2004 winners' medal, Stelios Giannakopolous could be forgiven if he had started thinking of winding down. Not at Bolton, though, where old glories are being revisited, and the Greek international has six goals and a key role in their push to fifth in the table.

* FOR FAILING TO DELIVER

Albert Luque has had his problems with injury but for ?9.5m he could at least try to look like he's enjoying the experience of swapping Galicia for Tyneside. Just the three Premiership starts for the 27-year-old so far and the feeling that Newcastle might not have signed him if they knew Michael Owen was coming.

* FOR SERVICES TO A GOOD CAUSE IN TRYING TIMES

Roy Keane has tried to keep trips outside his Cheshire home to a minimum, with so many television cameras parked outside, but he did gloriously eschew modern football tradition on one venture out. No designer labels, no sponsors' tracksuits, when Keane nipped to the garage he did so in his Irish Guide Dogs for the Blind jacket - one institution with no plans to dispense with his services.

* FOR DESTROYING A PERFECTLY GOOD SEASON

As soon as Charlton won five of their first six Premiership matches, Alan Curbishley was forced to answer questions about whether his side would fall prey to their usual late-season problems. He said he hoped it would be different this time and it certainly was: his players moved the slump forward to pre-Christmas and have now lost six of their last seven.

* FOR THE BRIEFEST OF APPEARANCES

The Barnet goalkeeper Ross Flitney was hit by a car - but not harmed - while jogging this month but if that sounds unlucky, you obviously never saw him at Old Trafford on 26 October. Two minutes into Barnet's big Carling Cup tie there and he was back on his own in the changing-room running a bath for one after a red card for handball outside the penalty area.

Sam Wallace's Fearless Predictions

* CHELSEA WILL WIN THE TITLE BY HOW MANY POINTS?

Eight

* SECOND, THIRD AND FOURTH WILL BE...

Manchester United, Liverpool, Arsenal

* WHO WILL WIN THE CHELSEA v BARCELONA TIE?

Barcelona

* AND WILL THEY GO ON TO WIN CHAMPIONS' LEAGUE?

You bet

* WHO WILL GO DOWN FROM THE PREMIERSHIP?

Sunderland, West Brom, Portsmouth

* FOOTBALLER OF THE YEAR (AT THIS STAGE)

Frank Lampard