Albion scored for the 30th successive Premier League game but their seven-match unbeaten run came to an end despite a herculean effort at Stamford Bridge.
Two goals in four first-half minutes by Enzo Fernandez and former Albion defender Levi Colwill appeared to put Chelsea in control but Facundo Buonanotte replied with his second goal for the club and before the break Chelsea had skipper Conor Gallagher sent off.
Fernandes gave the hosts breathing space with a 64th-minute penalty, awarded after referee Craig Pawson consulted the pitch side monitor, but Albion kept going. They had to wait until the first minute of stoppage time for their second goal when substitute Joao Pedro headed in his tenth of the season.
When Mr Pawson pointed to the spot after Simon Adingra’s cross hit Colwill it looked like they had the opportunity to draw level, but for the second time the official went to the monitor and for the second time it meant bad news for Albion, as replays showed the ball had hit Colwill’s head and not his arm.
At the end all the noise came from 3047 away fans, applauding the players for their efforts. It felt that 68% possession and nine shots on target deserved more of a reward.
Albion – with five changes from the side which secured Europa League progress on Thursday - began the game brightly with Adingra and Buonanotte both lively down the flanks while Jack Hinshelwood relished the task of trying to keep Raheem Sterling quiet.
But Chelsea suddenly found another gear to stun the Seagulls with two goals in three minutes.
They went ahead in the 17th minute when Albion couldn’t clear Gallagher’s corner on the right. Benoit Badiashile’s overhead kick back into the six-yard box found Fernandez who headed home from close range.
It was 2-0 when Jackson crossed from the left and Colwill’s close-range header went over the line despite Billy Gilmour’s acrobatic clearance.
It felt harsh that Albion were 2-0 down a quarter of the way into a contest where they had been very competitive, so the goal that got us back into it on 43 minutes was merited. Carlos Baleba and Adam Lallana were involved in the build-up but Buonanotte still had a lot to do when he picked up possession on the right-hand edge of the box but, cleverly using Colwill as a shield to unsight Rob Sanchez, he bent a left-foot shot past him and into the far corner.
Chelsea’s afternoon got worse moments later when Gallagher, who had already been booked for a hand in Buonanotte’s face, chopped down Billy Gilmour in midfield and the hosts were down to ten men. Evan Ferguson nearly levelled in stoppage time, his low drive from the left-hand corner of the bench going inches past the far post.
Momentum seemed to be with Albion and Adam Lallana went close to equalising when a delightful touch brought Adingra’s cross under control and he turned in an instant but his shot dropped a yard wide.
It was his last involvement as De Zerbi made a quadruple substitution with Kaoru Mitoma, James Milner, Joao Pedro and Pascal Gross adding experience to the mix.
Milner was involved on 64 minutes when Mykhailo Mudryk went down in the box under a combination of Jason Steele and Milner. The referee waved play on but was then advised to look at the monitor by VAR Jarred Gillett and a penalty was awarded, which Fernandez smashed down the middle to give Chelsea breathing space.
Albion regrouped and began to lay siege on the Chelsea goal. Mitoma forced Sanchez to save his looping header and a powerful low drive by Gross. By then Roberto De Zerbi had given Benicio Baker-Boaitey his Premier League debut.
Into ten minutes of stoppage time and Albion deservedly made it 3-2 when Joao flicked header from Milner’s corner flew into the far corner for his fourth goal in three games.
Now Sanchez earned his corn, saving Ferguson’s flick and a low drive by Joao before more controversy in the ninth of what turned out to be 15 minutes of stoppage time. Adingra’s cross hit Colwill and Pawson again pointed to the spot but this time he changed his mind after a trip to the monitor, the ball having struck Colwill’s head instead. Albion’s sense of injustice at the end was real.
Albion: Steele, Veltman, van Hecke, Igor (Baker-Boaitey 84), Hinshelwood (Milner 57), Adingra, Gilmour, Baleba (Gross 57), Buonanotte (Mitoma 57), Lallana (Joao 57), Ferguson.
Subs not used: Verbruggen, Moder, Kavanagh, O’Mahony.