Pascal Gross became Albion’s leading Premier League scorer with his 27th goal but West Ham replaced us at the top of the table with a 3-1 win.
We hadn’t lost in 12 previous games against the Hammers but 13 proved unlucky as West Ham, who had just 19% possession but counter-attacked ruthlessly, took control with goals from James Ward-Prowse, Jarrod Bowen and Michail Antonio before Gross set up a frantic finale with a goal ten minutes from time.
There was still time for Alphonse Areola to make world-class saves to deny Joel Veltman and Evan Ferguson but Albion suffered only their second Amex defeat since February.
Antonio and Pacqueta squandered early chances for the visitors when they went ahead in the 19th minute, just after Billy Gilmour drilled a yard wide from the edge of the box.
Adam Webster left a back-pass short and Antonio muscled in before picking out the unmarked Ward-Prowse for a close-range finish and his 50th Premier League goal.
Albion responded positively and Ferguson tested Areola after a lovely turn to create space before Ward-Prowse threw his body bravely in front of Gilmour’s full-blooded goalbound drive.
It had been a tough first half with West Ham suffocating Albion’s attack in the final third, but we nearly levelled a minute after the break when Mitoma’s cross picked out Ferguson whose powerful header was brilliantly pushed away by Areola.
Albion looked the more likely to score at that stage, only to be floored by two breakaway goals in six minutes.
On 58 minutes, Antonio’s pass from deep inside his own half found Said Benrahma and he spotted Bowen’s late run, found him with a low cross and Bowen’s excellent first touch cushioned the ball past Verbruggen and in off the far post.
It was 3-0 when Antonio latched onto Ward-Prowse’s ball down the channel, turned inside Webster and drilled his shot past Verbruggen and into the far corner.
But Albion refused to throw in the towel. Gross pulled one back with a low drive from the edge of the box ten minutes from time and only Areola’s brilliance denied them further goals when he diverted Veltman’s shot over before making an even better stop to push Ferguson’s powerful drive one-handed over the bar.
When Pervis Estupinan’s cross struck Vladimir Coufal and penalty appeals were ignored because the ball struck his supporting arm it summed up a frustrating evening for Albion, beaten at the Amex for only the second time since February.
Albion: Verbruggen, Milner (Veltman 72), Webster, Dunk, Estupinan, March (Adingra 72), Gilmour (Lallana 59), Gross, Mitoma, Welbeck (Pedro 59), Ferguson.
Subs not used: Steele, Julio, Dahoud, van Hecke, Buonanotte.
Referee: Anthony Taylor
Attendance: 31508