Bunny Shaw scored the only goal of the game at Kingsmeadow – her 14th WSL goal of the season – with a composed finish after only 14 minutes.
The Blues saw penalty appeals turned down in the first half, when Mayra Ramirez was caught by Alex Greenwood in the box.
They were also denied what looked a certain equaliser by a stunning double save from teenage goalkeeper Khiara Keating deep into second-half stoppage time.
After a rare home defeat for Chelsea, only goal difference now separates the teams in the standings, with eight league matches remaining until the conclusion of the campaign.
In her press conference on Thursday afternoon, Emma Hayes suggested there would be little to separate the WSL’s top two the following evening – and, for the first 10 minutes at least, that was the case. It was cagey; a slip-up could have grave implications for either team’s respective title chances.
With their first shot of the game, City took the lead. Gareth Taylor could be heard urging his side to press and the instructions bore fruit, as Jess Park caught Erin Cuthbert in possession and slipped the ball through to Shaw, who stayed composed as she drove forward and slipped the opener past Hannah Hampton.
Shaw almost had another soon afterwards, but Hampton beat the striker’s shot away after she was again found by a clever Park pass.
Meanwhile, Chelsea – who were uncharacteristically lacking fluency and potency in attack – were denied a penalty when Ramirez was caught by a last-ditch tackle from behind by Alex Greenwood. Had VAR been in operation in the WSL, the incident would certainly have been reviewed.
For the most part, the second half passed by without incident. Hayes made changes in an attempt to inject more energy and creativity, but her side had generated just 0.33 xG by the hour mark.
When captain Erin Cuthbert met a cut-back and flashed a curling shot across the face of goal, it became clearer it was not going to be the hosts’ night.
As City sat back to defend their precious in the nine minutes of added time at the end of the game, Chelsea did the opposite.
They almost benefitted from it, too, but 19-year-old Keating produced a great stop to keep out Jelena Cankovic after she caught a bouncing ball sweetly, and an even better one to deny Sjoeke Nusken as she followed up from point-blank range, securing City’s sixth clean sheet of the season and an eighth league win in succession.
