Graham Potter's expensively assembled side once again failed to live up to their price tags as the pressure mounted on the Blues boss.

Portugal forward Felix put Chelsea ahead in his second appearance for the club, only for Italy defender Emerson to haunt his former team with an equaliser before half-time.

Ninth-placed Chelsea have won just one of their past eight games in all competitions and are nine points adrift of the Premier League's top four.

Chelsea, without a win in their last seven away league games, splashed out more than £300 million ($362 million) on new signings during the January transfer window.

Although Potter insists he is well aware of the pressure to get Chelsea back on track, the former Brighton boss has been unable to stop the rot and is certain to face further scrutiny about his position.

The Blues face Borussia Dortmund in the Champions League last 16 first leg on Wednesday and Potter desperately needs to steer his team through to the quarter-finals to earn some breathing space.

Failing to beat lowly West Ham was another black mark against Potter, with the east Londoners sitting just two points above the relegation zone.

Felix returned for Chelsea following a three-game suspension and the on-loan Atletico Madrid forward posed an immediate threat when his goal was ruled out for a tight offside decision.

West Ham failed to heed that warning and Felix made them pay as he opened the scoring in the 16th minute.

- Chelsea stumble -

It was a goal entirely constructed by Chelsea's new recruits, with Mykhailo Mudryk snapping into a tackle on Jarrod Bowen before Enzo Fernandez curled his cross towards Felix, whose well-timed run beat West Ham's offside trap as he volleyed home from six yards.

Chelsea bossed the first half with the kind of composed display they have struggled to muster this term.

West Ham finally threatened when Kepa Arrizabalaga blocked Michail Antonio's back-heeled effort from Bowen's cross.

But Chelsea had lost their focus and the lead slipped from their grasp as well after 28 minutes.

It was a sloppy goal for Chelsea to concede as Vladimir Coufal was given too much time for a cross that was nodded on by Bowen to Emerson, who was left unmarked to scuff home at the far post.

Chelsea winger Noni Madueke, making his first start since signing from PSV Eindhoven in January, almost restored their advantage, cutting inside for a fierce strike that was well saved by Lukasz Fabianski.

Fabianski made another good save to keep out Felix's free-kick, while Antonio nearly headed Reece James' free-kick into his own net.

Chelsea struggled to find any rhythm in the second half and Potter sent on Mason Mount, Ben Chilwell and Hakim Ziyech.

West Ham thought they had won it with eight minutes left when Kepa pushed Declan Rice's header to Tomas Soucek, but the midfielder's tap-in was disallowed for offside against Rice.

Conor Gallagher's shot hit Soucek's arm in stoppage-time, but VAR refused to give the penalty.