Defending champions Manchester City beat injury-hit Chelsea 1-0 on Thursday to close the gap on Premier League leaders Arsenal to just five points.
Pep Guardiola's men were well below par in the first half but were transformed after the break, with substitutes Jack Grealish and Riyad Mahrez combining for the only goal, scored by the Algerian in the 63rd minute.
Graham Potter's Chelsea came into the game at Stamford Bridge languishing in 10th place in the table but they had the better of the opening 45 minutes.
However, it was a different story in the second half as the visitors found their attacking rhythm, with Guardiola admitting they were "miles better in every department" after the break.
"We struggled a lot in the first half -- it was sloppy and slow and without rhythm," the City boss told Sky Sports. "In the second half it was much, much better from minute one.
"The three points are important, definitely. The players know it. For a long time we were at the top. But we try, we have the FA Cup and Carabao (League) Cup and then Old Trafford. But it's important for these games, a win today."
Chelsea, already without a clutch of senior players including Mason Mount and Reece James, lost forward Raheem Sterling to an apparent hamstring injury in the opening minutes, replaced by Pierre-Emerick Aubameyang.
The home side were first to threaten seriously but City defender John Stones came to the rescue in the 16th minute as Christian Pulisic bore down on goal, producing a perfectly timed sliding tackle to deny the US forward.
The American was injured in the challenge and was forced off minutes later, compounding Chelsea's problems.
Teenager Carney Chukwuemeka, who came on for Pulisic, almost made an instant impact but his shot was blocked and Hakim Ziyech's effort was saved by City goalkeeper Ederson.
Erling Haaland, who has 21 Premier League goals this season -- one more than the entire Chelsea side -- smashed a shot wide in the 38th minute on what proved to be a quiet evening for the Norwegian superstar.
But Chelsea continued to look the more dangerous side and came agonisingly close to breaking the deadlock when Chukwuemeka hit the post just before half-time.
- Double change -
Guardiola, unhappy with what he had witnessed, made a double substitution at the interval, bringing on Rico Lewis and Manuel Akanji for Joao Cancelo and Kyle Walker in the search for more control.
The visitors immediately settled and began to dictate play, with Nathan Ake heading against the woodwork, but Chelsea responded well and were inches away from taking the lead when Thiago Silva flashed wide.
Guardiola, whose team drew 1-1 with Everton at the weekend, introduced Grealish and Mahrez on the hour mark to further freshen up his attack.
The decision paid dividends minutes later when Grealish produced an excellent pass from the left and Mahrez prodded home from close range.
Potter made changes of his own, bringing on England forward Conor Gallagher, but they were unable to find an equaliser despite some late pressure.
The result leaves City five points behind Arsenal, who dropped points in a 0-0 draw against high-flying Newcastle earlier in the week.
But Potter is under increasing pressure -- Chelsea now have just one win in their past eight league games and remain 10 points off the top four.
Potter, whose Chelsea side face City again in the FA Cup third round at the Etihad on Sunday, said he was proud of his team's performance, especially after losing Sterling and Pulisic so early.
"It's tough at the moment I must admit and I feel for the boys," he said.
"We have to stick together. It was disappointing to lose those guys but the players on the pitch and the ones that came in gave everything and that's all you can ask for."