Chelsea fought back from 3-0 down to earn a point at West Brom and make up for a first-half defensive horror show at the Hawthorns.
A catalogue of errors left Chelsea 3-0 down at half-time, with Callum Robinson opening the scoring with a low drive into the far corner from 15 yards after Marcos Alonso's initial sloppy header (4).
Tammy Abraham missed a glorious chance to equalise, before Timo Werner hit the crossbar, but Robinson soon had West Brom 2-0 up against the run of play, pouncing on Premier League debutant Thiago Silva's miscontrol to slot below Willy Caballero (25).
Kyle Bartley turned home from a corner at the far post following some woeful Chelsea marking (27) to make it 3-0, but the visitors improved in the second half as Mason Mount's long-range strike (54) and sub Callum Hudson-Odoi's fine finish (70) brought them to within a goal of a special comeback.
And it was completed in the third minute of stoppage time as Abraham capitalised to tap home after Sam Johnstone had parried Mount's low effort, crippling West Brom after they looked to have fought off the Chelsea onslaught.
But for all of Chelsea's spending at one end of the field, it was their issues at the other that nearly cost them again, and neither side seemed happy at full-time following another high-scoring Premier League thriller.
- Chelsea defence in disarray
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West Brom: Johnstone (6), Furlong (6), Bartley (6), Ajayi (6), O'Shea (7), Townsend (6), Pereira (7), Livermore (6), Saywers (6), Diangana (7), Robinson (7)
Subs: Robson-Kanu (6), Phillips (5), Field (NA)
Chelsea: Caballero (5), James (5), Christensen (5), Silva (4), Alonso (4), Kante (5), Kovacic (5), Mount (7), Kavertz (6), Abraham (6), Werner (6)
Subs: Azpilicueta (7), Hudson-Odoi (7), Giroud (6)
Man of the match:Mason Mount
How Chelsea recovered from first-half shocker
Frank Lampard had big decisions to make in his team selection, starting Caballero over Kepa Arrizabalaga, with new signing Edouard Mendy not yet available, while defender Silva made his Premier League debut and was made captain.
Lampard explained how Silva's leadership qualities earned him the armband, but Chelsea were all over the place in the first half as West Brom reacted with glee to their sloppy defending.
Alonso was at fault for the first, tamely heading the ball into the path of Matheus Pereira, who drove forward and released Robinson on the left of the box. The striker had plenty to do, but found the far corner past Cabellero from an angle for the opener.
Chelsea initially reacted well - Abraham missed a glorious chance at the far post from Reece James' delivery, while Werner struck the crossbar from another James centre - but it was Albion who scored next against the run of play.
Receiving the ball back from Alonso, Silva's miscontrol allowed Robinson to pounce, and after pacing into the area and composing himself, he struck low under Cabellero to stun Chelsea.
The third may have enraged Lampard the most; Pereira's driven corner looked straight off the training ground as Darnell Furlong dropped deep to flick on, and his header found Bartley at the far post to turn home, completely unmarked and onside.
James, who was finding space in the final third and accounted for 12 of the 17 first-half cross across both sides, was guilty of giving too much space to Bartley on that occasion.
Frank Lampard gave Thiago Silva his Premier League debut - and as captain - and also named Willy Caballero in the starting XI at the expense of Kepa.
Tammy Abraham started up front with Werner, with Jorginho dropping to the bench. Christensen was back from suspension, meaning Zouma was the man to drop out.
For West Brom, the suspended Gibbs was replaced by Townsend in the only change from the 5-2 defeat at Everton.
Lampard made two changes at the break - Cesar Azpilicueta on for Alonso and Callum Hudson-Odoi for Mateo Kovacic - and it triggered some hope for Chelsea as Mount received Azpilicueta's pass before lashing a fine strike into the bottom left corner from 25 yards.
Chelsea piled forward and got their second with a fine team goal as Hudson-Odoi slotted low into the far corner following a neat one-two with Havertz inside the box.
And the pressure told late on as Mount's low effort from inside the box was parried by Johnstone, handing the ball on a plate to Abraham to pounce a few yards out. There was a big shout from West Brom for handball by Havertz in the build-up, but because the German didn't make the immediate assist, the goal wasn't ruled out.
What the managers said...
West Brom boss Slaven Bilic: "I'm happy with our performance. To score three against Chelsea is something. I'm very proud of the boys, we have to build on this to get the confidence and the spirit so we can see that we can play against a team who is individually better than our players - but that we can defend against them and that we can play some good football and create chances."
Chelsea boss Frank Lampard: "It's two points lost. That's no disrespect to West Brom, but to come here and understand the game and know transition and mistakes would be something they would jump on, counter-attack against us, and set-pieces.
"We spoke about it before the game, you can't legislate for pure mistakes, but that gives you a really difficult game to get back into. I can laud character, because we showed character and persistence, but we wouldn't need to if we didn't make those mistakes.
Chelsea's defensive woes in stats
- Since the start of last season, Chelsea have conceded more away Premier League goals than any other team (42).
- Chelsea have conceded 3+ goals in successive Premier League away games against newly-promoted sides for the first time since March 1997 (v Sunderland and Derby).
- Chelsea have failed to keep a clean sheet in 20 of their 21 Premier League away games under Frank Lampard.
- Chelsea defender Thiago Silva is the first outfield player to make an error leading to a goal on their Premier League debut since Issa Diop for West Ham versus Arsenal (August 2018).
Live EFL Cup
West Brom now go to Southampton in the Premier League on Sunday at midday, while Chelsea are at Tottenham in the Carabao Cup fourth round on Tuesday at 7.45pm, live on Sky Sports Football, before hosting Crystal Palace in the Premier League on Saturday at 12.30pm.