BBC Sport looks back on one of the most exciting Premiership title battles in recent years.
Chelsea started the season bolstered by the summer acquisitions of Andrei Shevchenko and Michael Ballack.
31 August 2006
1st: Man Utd P3 W3 D0 L0 9pts
5th: Chelsea P3 W2 D0 L1 6pts
And after a defeat by Liverpool in the Community Shield, Chelsea made an impressive start to their Premiership campaign with a 3-0 home win over Manchester City.
But the Blues slipped up in their second game, losing at Middlesbrough before beating Blackburn away from home. The previous season Jose Mourinho's team had gone 11 Premiership games before tasting defeat.
Man Utd started the season in top form
Manchester United had brought in Michael Carrick but sold Ruud van Nistelrooy, while uncertainty surrounded the future of Cristiano Ronaldo following his role in the dismissal of Wayne Rooney during England's 2006 World Cup quarter-final with Portugal.
But United started August by making an emphatic statement of intent.
A 5-1 home win over Fulham was followed by victories against Charlton and Watford as United ended August with maximum points - and a three-point lead over Chelsea.
The most significant date in September was the 17th.
Chelsea beat Liverpool, while United lost for the first time in the Premiership, a 1-0 defeat at home to Arsenal.
30 September 2006
1st: Chelsea P7 W5 D1 L1 16pts
3rd: Man Utd P6 W4 D1 L1 13pts
The defeat ended United's run of four straight Premiership wins - and they dropped to second place as a consequence, while a draw with Reading in their next fixture led to them slipping down another place.
Chelsea finished the month on top of the table, although United's 2-0 win over Newcastle on 1 October took them back to first place on goal difference and ensured that the two title rivals had each won five, drawn one and lost one of their opening seven games.
The Premiership resumed on 14 October after a break for international fixtures - and both teams were in prime form.
31 October 2006
1st: Man Utd P10 W8 D1 L1 25pts
2nd: Chelsea P10 W8 D1 L1 25pts
Chelsea defeated Reading, Portsmouth and Sheffield United, while United overcame Wigan, Liverpool and Bolton.
But of huge significance was the injury to Chelsea's inspirational keeper Petr Cech, who sustained a fractured skull at Reading that kept him sidelined for several months.
Cech missed several months with a head injury
Both teams ended October with 25 points, although United had opened up a superior goal difference, having scored 23 to Chelsea's 17 and with both teams having conceded five.
United and Chelsea would occupy the top two places for the remainder of the season while the goal difference would continue to heavily favour the men from Old Trafford.
By the end of November the chase for the title already had the look of a two-horse race.
Chelsea's trip to Man Utd was keenly contested - and finished 1-1
Liverpool goalkeeper Pepe Reina admitted as much as early as 15 November when he said: "The Championship is probably too far away for us because mathematically Manchester United and Chelsea are very superior."
Arsenal and Liverpool finished the month in sixth and seventh places respectively - both 13 points behind second-placed Chelsea and 16 adrift of leaders United.
Chelsea travelled to Old Trafford to play United on 26 November - the match ending in a 1-1 draw.
30 November 2006
1st: Man Utd P15 W12 D2 L1 38pts
2nd: Chelsea P15 W11 D2 L2 35pts
But United, who won their other four fixtures, had extended their lead to three points by the end of the month, with Chelsea having lost at Tottenham on 5 November.
Chelsea found themselves eight points adrift of United after a draw with Arsenal on 10 December - although they had a game in hand and Mourinho was in bullish mood.
Of the title race, Mourinho warned: "If Ferguson thinks it's over he's in trouble because it's not."
Michael Essien also made it clear what he thought of United.
Ronaldo shows the strain after defeat at West Ham - but the month belonged to United
"We are much better than Manchester United," said the Ghana international.
"It is just a matter of days before we are the leaders. I have done the calculations and we will finish at least five points clear of United at the top of the table."
Ferguson warned his players against complacency - and wisely so, since Chelsea went on to win their game in hand, a 1-0 victory over Newcastle.
United's 12-game unbeaten run ended in a 1-0 defeat at West Ham in Alan Curbishley's first game at the helm of the struggling Hammers on 17 December.
Hours later Chelsea scored two late goals to beat Everton 3-2, closing the gap to two points.
Ferguson opined "I'm not sure they are on a charge" but Chelsea seemed to have a real sense of momentum.
However, another crucial injury would undermine Chelsea's attempt to close the gap on their rivals.
Inspirational skipper John Terry had missed the match against Everton after suffering a recurrence of a back injury.
31 December 2006
1st: Man Utd P21 W17 D2 L2 53pts
2nd: Chelsea P21 W14 D5 L2 47pts
The talismanic figure was ruled out of the busy festive period and his absence was keenly felt as Chelsea conceded two goals in each of their last four league matches of 2007, drawing two of them.
Worse still, Chelsea announced on 28 December that Terry had undergone surgery to remove a sequestrated lumbar intervertebral disc.
He would be out for some time.
United, in stark contrast, enjoyed a happy Christmas, winning three matches after the defeat by West Ham with Ronaldo, whose future was in doubt several months earlier, scoring twice in each game to take his tally for the season to 12.
The year ended with United six points clear of Chelsea.
January heralded the opening of the transfer window - although United had already announced some time earlier the short-term arrival of Henrik Larsson on a loan deal from Helsingborg.
The problems all seemed to belong to Mourinho, who started the year by claiming: "In this moment Chelsea cannot defend. I am the first to know that."
Robert Huth and William Gallas had left the club the previous summer and, with John Terry now sidelined, Mourinho, for all his expensive purchases, found himself short of central defenders.
Mourinho had precious little to smile about in January
Yet the Chelsea boss let it be known that his requests to bolster his squad had fallen on deaf ears - and stories began to appear suggesting he would not be at the club beyond the end of the season.
Blues chief executive Peter Kenyon claimed on 9 January that there was "absolutely no truth" in the rumours.
The poor form of Mourinho's big summer-signings Shevchenko and Ballack was not helping the situation but Mourinho nonetheless found time to taunt Ferguson.
Speaking on 3 January, Mourinho said: "Considering the problems Chelsea have had, Manchester United should be 10, 12, 14 points clear of us. I am happy to be six points behind.
"In my opinion, Manchester United did not take advantage of our bad moments."
But the bad moments did continue - with Chelsea losing 2-0 at Liverpool, while Terry, despite persistent rumours of his imminent return, remained sidelined for the rest of the month.
31 January 2007
1st: Man Utd P25 W19 D3 L3 60pts
2nd: Chelsea P25 W16 D6 L3 54pts
Thankfully for Chelsea, United failed to capitalise on the defeat at Anfield, instead losing 2-1 at Arsenal the following day.
United led 1-0 with seven minutes left but conceded two late goals.
They ended the month six points clear but it could so easily have been nine, while Cech had returned from his lengthy injury against Liverpool and was back in goal for the Blues.
Chelsea only played two Premiership games in February - winning both of them.
Terry returned at the start of the month and the Blues won the first trophy of the season, the Carling Cup, with a victory over Arsenal.
28 February 2007
1st: Man Utd P28 W22 3 L3 69pts
2nd: Chelsea P27 W18 D6 L3 60pts
United took full advantage of Chelsea's participation in that competition by winning all three Premiership fixtures they played - extending their lead to nine points, having played one game more but with a vastly superior goal difference.
It might have been only seven points had the irrepressible Ronaldo not scored a late winner at Fulham on 24 February.
No more could have been asked of Chelsea in March.
With lynchpins at the back, Cech and Terry, having returned to the fold, Chelsea won all four of their Premiership fixtures - including their game in hand on United.
It was superb form under extreme pressure - and from a team that had looked to be faltering at the turn of the year.
United could be forgiven for believing they had dealt a major blow to Chelsea when John O'Shea's injury-time goal gave them a 1-0 win at Liverpool on 3 March.
Kalou is mobbed by team-mates after his winner at Watford
It was the early kick-off that day and put United 12 points clear. However, only hours later Chelsea showed their mettle with a 2-0 win at Portsmouth before winning their game in hand - against Manchester City - to close the gap to six points.
Didier Drogba scored the opening goal against Pompey on 3 March to take his Premiership tally to 18.
After an unspectacular first season in the Premiership, his second was a revelation and the Ivorian was battling for the Premiership's Golden Boot with Ronaldo, who at the same stage of the season had scored 16 goals.
It almost turned sour for Chelsea at rock-bottom Watford on 31 March before Salomon Kalou popped up with a last-minute winner.
31 March 2007
1st: Man Utd P31 W25 D3 L3 78pts
2nd: Chelsea P31 W22 D6 L3 72pts
Mourinho admitted afterwards that dropping more points would have effectively handed the title to United.
United, in addition to beating Liverpool, won their other two Premiership fixtures, beating both Bolton and Blackburn 4-1.
But key defenders Gary Neville and Nemanja Vidic had picked up injuries during the month - stretching United's resources at a crucial time.
Chelsea opened April with their eighth and ninth consecutive Premiership victories.
United, in contrast, suffered a defeat at Portsmouth at the start of the month - a loss that reduced their lead to three points and with the Red Devils set to visit the Blues on 9 May.
30 April 2007
1st: Man Utd P35 W27 D5 L4 85pts
2nd: Chelsea P35 W24 D8 L3 80pts
The result blew the title race wide open and Ferguson called on his players to hold their nerve.
"We have showed character all season and must do so again now," he said.
But his team slipped up again, drawing 1-1 with Middlesbrough at Old Trafford on 21 April and afterwards Ferguson admitted the result had "opened the door".
Plus, during the match Rio Ferdinand limped off with a groin problem, prompting Ferguson to talk of an injury crisis of "massive proportions".
The following day Chelsea had the chance to close the gap to one point but were held to a goalless draw at Newcastle.
Mourinho was at his belligerent best afterwards, arguing that his team were having to contend with "new football rules" because "it is not possible to have a penalty against Manchester United".
He was referring to penalty claims by Sheffield United and Middlesbrough that had been turned down in recent games at Old Trafford.
Ferguson responded in no uncertain terms, stating: "Mourinho seems to be on some sort of personal crusade. We have four games to go now. If we get a penalty against us, Mourinho wins that war. That is wrong."
And so came what proved to be the decisive weekend of the season.
Ferguson (right) was delighted after the crucial win at Everton
Unusually, Chelsea and United both kicked-off at the same time, 1245 BST on Saturday 28 April.
After conceding a goal, Chelsea came from behind to go 2-1 ahead against injury-ravaged Bolton, while Everton took the lead against United - a situation that left Mourinho's team level on points with their title rivals.
But Bolton equalised after the break and, although Everton doubled their lead, United staged a brilliant comeback to win 4-2.
Ferguson danced on to the Goodison Park pitch at the end, clapping his hands. Stamford Bridge was eerily silent at the final whistle.
Mourinho argued the title race was "not over" but, with only three games left for each team, United appeared to have a decisive five-point advantage, allied with a hugely superior goal difference.
It was a bleak start to May as both teams suffered Champions League exits at the semi-final stage.
United shrugged off the hugely disappointing 3-0 second-leg defeat at AC Milan by winning 1-0 in a local derby at Manchester City.
After losing a penalty shoot-out at the hands of Liverpool, Chelsea faced a daunting trip to Arsenal.
They were up against it after Khalid Bouhlarouz was dismissed for a professional foul on Julio Baptista moments before half-time, with Gilberto Silva dispatching the penalty.
Despite a gallant second-half display at the Emirates during which Michael Essien levelled, the Blues could not find the winning goal which would have prolonged their title challenge.