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
5. Lewis Dunk - 7
Took no chances up against Bowen and kept to his tasks well. Found in space at the back post but his pull back was cut out. Went up for a header which led to the opening goal. Vital block at 1-1. Photo: Alex Broadway/Getty Images
6. Pervis Estupinan - 6
Beaten by Bowen but keeper came to the rescue. Slipped at crucial moment as he looked set to at least the test the keeper. Just about summed up the first half. Did well to work space on edge of his own box and start a counter attack. His cross resulted in Wieffer’s goal. Kudus was too quick to stop for the equalising goal. Set up Ayari for big chance. Booked for rash tackle. Photo: Alex Broadway/Getty Images
7. Mats Wieffer - 8
A big chance to impress with a rare start – and he took it with open arms. Good on the ball and looked more confident. Did his defensive duties well early on. Grabbed his first Albion goal to open the scoring – huge moment for him after a difficult start to life on the south coast. Such a shame he had to go off injured minutes later and it could have led to West Ham levelling. Photo: Alex Broadway/Getty Images
8. Carlos Baleba - 6
Created chance for Mitoma. Formed a nice midfield partnership with Wieffer in the double pivot. Classy in moments but not at his very best at the moment. Photo: Bryn Lennon/Getty Images