Chelsea's search for successive Premier League wins this season goes on after James McClean's late strike earned West Brom a 2-2 draw at Stamford Bridge.
Cesar Azpilicueta's goal was cancelled out by substitute Craig Gardner before Gareth McAuley deflected Willian's cross into his own goal.
The Baggies came from behind for a second time when Irish winger McClean struck four minutes from time as the Baggies earned a deserved point.
Chelsea felt aggrieved and Diego Costa made his frustrations known at the final whistle by arguing with Baggies players.
Costa felt Claudio Yacob, already booked for a first-half foul, should have received a second yellow card for an off-the-ball trip on him early in the second half.
The midfielder was promptly substituted and referee Anthony Taylor barracked by Chelsea players and supporters thereafter.
The Blues are unbeaten in six games since the departure of Jose Mourinho, but Guus Hiddink's hopes of a top-four finish receded further in front of owner Roman Abramovich and ahead of Saturday's clash with Everton.