Brighton heaped more pressure on West Ham manager Slaven Bilic with a 3-0 Premier League win at London Stadium, their first away from home this season.
Hammers fans booed throughout and thousands left the ground following Brighton’s third goal.
The defeat means West Ham slipped to 17th in the table and will drop into the relegation zone if Leicester beat Swansea on Saturday.
Brighton took the lead after 10 minutes when the unmarked Glenn Murray headed in Pascal Gross’ free-kick.
Moments before the break Jose Izquierdo curled past Joe Hart from distance, despite the England goalkeeper getting a strong hand to the ball.
Murray added his second from the penalty spot in the 75th minute after he was fouled by Pablo Zabaleta.
Although they dominated possession, the Hammers had only two shots on target, long-range efforts from Pedro Obiang and Manuel Lanzini.
Pressure back on Bilic
After losing their first three games of the season, resulting in calls for Bilic to be sacked, West Ham claimed eight points from their next five matches.
However, before the game the Croat talked of possible “hurricanes” if results went badly, and he can expect to come under more scrutiny after his side’s awful performance here.
Former England midfielder and BBC Radio 5 live pundit Jermaine Jenas said the Hammers were “embarrassed” by their opponents and that the performance felt like the “final nail in the coffin” for Bilic.
The crowd grew more restless throughout as passes were misplaced, crosses failed to find a team-mate – West Ham attempted 33 – and shots went hit high and wide.
The marking for Murray’s opening goal from 10 yards was non-existent, while Hart will be questioned for palming Izquierdo’s strike into the net as he dived to his left.
“He has got that much of his hand on the ball that he has got to save it,” Jenas said.
Brighton break away duck
Victory for Brighton – their first on the road in the top flight since 1983 – resulted in jubilant scenes at the final whistle.
However poor West Ham were, Brighton defended resolutely and were impressive in attack.
They scored three goals from seven attempts – West Ham had 16 efforts – and could have added further misery to their hosts as Murray had two good chances saved by Hart.
Brighton centre-backs Lewis Duffy and Shane Dunk were excellent, making 11 clearances each to ensure goalkeeper Mat Ryan was hardly tested.
Victory was Hughton’s first away from home in the Premier League since November 2013, ending a run of 12 matches without a win.
Brighton’s dizzy heights – the best stats
Brighton recorded their joint-biggest away top-flight win, equalling their 3-0 victory at Crystal Palace in April 1981.
This was West Ham’s heaviest home league defeat against a newly promoted side since losing 5-1 to West Bromwich Albion in November 1931.
The Seagulls end the day in the top half of the top flight outside the month of August for the first time since October 1982.
Pascal Gross has assisted four goals in his first nine Premier League matches. Of players to have played their first nine games for a newly promoted side, no player has more (level with Tommy Wright, Wayne Routledge, Adam Lallana and Jobi McAnuff).
Since Slaven Bilic took charge of West Ham, the Hammers have conceded 18 penalties in the Premier League, four more than any other side.
Glenn Murray has twice scored two goals in a Premier League game – both against West Ham (he scored twice for Crystal Palace in February 2015).
West Ham have conceded more headed goals than any other Premier League side this season (5). They conceded four headed goals in Slaven Bilic’s first season in charge in 2015-16.
No side has conceded more set-piece goals in the Premier League this season than the Hammers (6, level with Watford).