Manchester City have moved to within five points of leaders Arsenal in the Premier League table courtesy of a 1-0 win over Chelsea at Stamford Bridge.
Riyad Mahrez came off the bench to score the only goal of the match, with the Algeria international finding the back of the net in the 63rd minute, converting a cross from fellow substitute Jack Grealish.
Second-placed Man City have moved to within five points of Arsenal, while Chelsea remain down in 10th, 10 points behind fourth-placed Manchester United on the same number of games (17).
The two teams will again lock horns on Sunday afternoon, with Pep Guardiola's side hosting the Blues in the third round of the FA Cup.
Chelsea were forced into a change in just the fifth minute of the contest, with Pierre-Emerick Aubameyang replacing the injured Raheem Sterling, who did not have the chance to potentially star against his former club.
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The first half-chance of the match came for the hosts in the 16th minute when Kai Havertz found Christian Pulisic inside the Man City box, but John Stones was across to make an excellent challenge.
Chelsea then had to make a second substitution in the 22nd minute, with Carney Chukwuemeka replacing the injured Pulisic, but it was the home side that continued to look the most likely to score.
Chukwuemeka had a half-chance shortly after entering, with Havertz finding the youngster inside the Man City box, but the midfielder was denied by a last-ditch challenge from Stones.
Ilkay Gundogan placed one wide of the Chelsea post in the 32nd minute, with Man City enjoying more of the ball, but the champions were finding it difficult to carve out clear openings.
Erling Braut Haaland's first sight of the Chelsea goal came in the 37th minute, but the Norway international could only poke the ball over the crossbar under pressure.
The hosts hit the post in the 43rd minute through the lively Chukwuemeka, with the midfielder working his way to the edge of the box before attempting to pick out the back of the net, but it deflected onto the woodwork.
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A lively end to the first period then saw Kevin De Bruyne have an effort deflected behind for a corner, but the half-time whistle blew with the two teams level at 0-0.
Man City made two changes at the interval, with Manuel Akanji and Rico Lewis replacing Kyle Walker and Joao Cancelo.
Haaland had a half-chance early in the second half after as loose pass from Aubameyang was intercepted, but the striker's effort was deflected wide of the post.
Nathan Ake then headed against the crossbar from close range after meeting a brilliant cross from De Bruyne, before Kepa Arrizabalaga had to keep out a low strike from Man City's Belgium international, with the visitors much improved at the start of the second period.
Chelsea had a huge chance of their own in the 56th minute, but Thiago Silva could only fire wide of the goal from inside the box after a period of panic inside the Man City box.
De Bruyne then fired wide of the Chelsea goal just before the hour, with both sides having opportunities during a lively period of the match.
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Man City made the breakthrough in the 63rd minute of the contest, and it was the two substitutes that combined, as Grealish delivered a brilliant low cross into Mahrez, who simply could not pass up the chance to send his side into the lead.
Aubameyang, who was an early substitute, was replaced as part of a triple Chelsea change in the 68th minute, with Omari Hutchinson, Lewis Hall and Conor Gallagher entering the field.
Haaland came close to converting a low cross from De Bruyne in the 73rd minute, and the home side did take the match to the champions in the period that followed, with Gallagher's high-energy work raising the crowd.
Hall had a brilliant chance to level for Chelsea in second-half stoppage time after being released in a dangerous position, but the youngster fired over the crossbar, as Man City claimed a vital three points in London.
Chelsea's next Premier League match will be against London rivals Fulham on January 12, while Man City will be back in league action against an in-form Manchester United at Old Trafford on January 14.
Matt Law
