Manchester City will head into the new year with an eight-point lead at the top of the Premier League, after Phil Foden's first-half goal earned them a 1-0 win at Brentford on Thursday (NZ time).
Foden stroked home in the 16th minute from Kevin de Bruyne's pass and it proved sufficient to seal a 10th successive league win for Pep Guardiola's relentless champions.
With Liverpool losing at Leicester City on Wednesday and Chelsea held by Brighton and Hove Albion on Thursday, City have seized complete control of the title race.
They were far from their slick best in west London, however, with Brentford always looking capable of salvaging something.
De Bruyne did hit the post after the break, and both Foden and Aymeric Laporte had goals disallowed, as City sought to give themselves a cushion.
But City held on with few real scares to reach 50 points from 20 games, with Chelsea on 42 from 20 and Liverpool on 41 having played one game less than the top two.
Chelsea suffered another stumble in their faltering title challenge, when they were held to a 1-1 draw at home by Brighton and Hove Albion after an injury-time equaliser by substitute Danny Welbeck.
The European champions had taken the lead, when Romelu Lukaku rose the highest to meet a corner from Mason Mount in the 28th minute, taking advantage of a makeshift Brighton defence that was missing centre-half stalwarts Lewis Dunk and Shane Duffy.
But Brighton pushed hard for their first ever goal at Stamford Bridge and had Chelsea pinned back in the second half.
Just when the Blues seemed as if they were going to hang on for three vital points, Welbeck rose between defender Toni Rudiger and Trevoh Chalobah to head in a Marc Cucurella cross.
Compounding Chelsea's problems, Chelsea wing-back Reece James hobbled off in the first half and fellow defender Andreas Christensen also needed treatment and was replaced by Chalobah at the break.