The Hammers had not beaten the Seagulls since their promotion to the Premier League – a run that spanned six years and 12 games.
However, goals from James Ward-Prowse – his first for the Irons and 50th in the Premier League – Jarrod Bowen and Michail Antonio secured a fine victory for David Moyes’ side.
Alphonse Areola was in inspired form for the Hammers but was finally beaten when Pascal Gross found the corner with an inch perfect strike from outside the box, with ten minutes remaining.
Evan Ferguson and Lewis Dunk went close in injury-time but it was too little, too late for Albion, who were a shadow of the side that dismantled Wolves and Luton.
Here’s how Roberto De Zerbi’s players rated:
. Brighton 1-3 West Ham
West Ham put on a counter attacking masterclass as they recorded their first ever Premier League victory over a below-par Brighton. Photo: Henry Browne/Getty Images
. Bart Verbruggen - 5
Not the way he would have wanted his first Premier League game to go. Made a few comfortable saves but couldn't stop any of the goals. In fairness, he wasn't really helped by his defenders Photo: Charlie Crowhurst/Getty Images
. James Milner - 5
Looked a bit leggy in the first half and struggled to keep up with West Ham's pacey attackers. Involved in a heated exchange, showing he's still got that fire in his belly. Looking to make an impact going forward. Good effort saved as Albion looked to fight back from three goal down Photo: Charlie Crowhurst/Getty Images
. Lewis Dunk - 6
Not his best game for Brighton but was among the better performers on the pitch. Was too casual in certain moments. Two cracking headers kept out by an inspired Alphonse Areola and another cleared off the line by a defender. Photo: Henry Browne/Getty Images
. Adam Webster - 3
Webster won't look back at this game with any fondness. He was at fault for the first goal after being bullied off the ball by Antonio. He wanted a foul but it was never going to be given. Gave Benrahma far too much time and space to find a cross for the second goal, finished off by Bowen. The defender was beaten again by Antonio for the third goal. Not a good day at the office for the defender Photo: Henry Browne/Getty Images
13. Substitutes' ratings
Yankuba Minteh – 7: Couldn’t quite keep Baleba’s long ball in play. At the heart of a huge chance, as the ball hit the post and somehow didn’t go in to make it 2-1 to Brighton. Wasteful cross shortly afterwards. Excellent cross was begging to be put in after he did so well to keep hold of the ball out side | Yasin Ayari – 6: Offered something a bit different but not enough to get the win. Deflected effort on goal was saved. Shot saved at point blank range – far too close to the keeper | Tariq Lamptey – 6: Clumsy foul on Summerville but looked decent going forward – given the freedom to go at West Ham’s defenders. Brave header on goal with the clock ticking down and he was taken out. | Julio Enciso – 6: Energetic when he came off the bench this afternoon, as he looked to follow up on a positive performance against Crystal Palace, which earned praise from his manger. Had a shot saved comfortably before playing a lovely ball in for Lamptey – but West Ham were able to clear. Just not able to unlock the key today. | Evan Ferguson – 6: Mistimed an effort on goal when he looked destined to score on the 88th minute. Threw himself at Minteh’s cross just after. Good to see him getting in the right places and the goals will soon return. Great hold up play to set up Ayari, who should have scored. Photo: Bryn Lennon/Getty Images