Branislav Ivanovic scored the goal that sunk Manchester City at the Eithad Stadium tonight.
His first half strike, a beautiful left-footed daisy-cutter was enough to consign City to their first home league defeat of the season.
Chelsea remain in third place but are level on points with City and just two behind Arsenal, who still have to visit Stamford Bridge. The North Londoners have 55 points.
This was a masterclass of counter-attacking play by Mourinho, but it want a park the bus in front of the side who had won a straight 11 league victories at home .
Chelsea fully deserved their victory and even hit the woodwork three times through Samuel Eto'o, Nemanja Matic and Gary Cahill. They could, and should, have won by a greater margin.
Jose Mourinho still believes that his side won't win the league this season, and the sloppy defeats at the hands of Newcastle and Stoke suggest that the title probably won't be returning to SW6 in the coming months.
The inability to see off West Ham United at the weekend highlighting the weakness up front that will need to be addressed in the summer.
Had Chelsea secured the services of a seriously top-quality striker this season, rather than the fading Samuel Eto'o and Fernando Torres to complement the average Demba Ba, then the Blues would be out of sight by now at the head of the league.
In a cold analysis of the weekend's matches the real winners are Arsenal who remain on top.
The Blues face Newcastle United on Saturday who were hammered at home by arch rivals Sunderland 3-0.
Their director of football Joe Kinnear resigned tonight.
Chelsea (4-2-3-1):Cech; Ivanovic, Cahill, Terry (c), Azpilicueta; D Luiz, Matic; Ramires, Willian (Mikel 90+1), Hazard (Ba 90+3); Eto'o (Oscar 83).
Unused subs Schwarzer, Cole, Lampard, Salah.
Scorer Ivanovic 31.
Booked Ivanovic 32, Matic 39, Willian 90+1.
Man City (4-4-2):Hart; Zabaleta, Kompany,Nastasic, Kolarov,; Navas, Toure, Demichelis, Silva; Negredo (Jovetic 56), Dzeko.
Unused subs Pantilimon, Clichy, Boyata, Milner, Rodwell, Lopes.
Booked Demichelis 36, Kolarov 41, Nastastic 87.
Referee Mike Dean