David Moyes' men continue their poor Premier League form with a third loss in as many games.
West Ham have yet to score in the league and they did not look much closer against Brighton on Sunday, as Michail Antonio, Jarrod Bowen and newcomer Gianluca Scamacca were held back by a solid Graham Potter side.
Brighton were the better team, which is mirrored by the player ratings.
West Ham
Lukasz Fabianski - 5/10
The West Ham number one could not do much to stop Brighton scoring their two goals. He was not tested much otherwise.
Vladimir Coufal - 6/10
Worked his boots off as usual but found it hard to impact West Ham's attacking play. The Czech international was later subbed off after a head injury.
Kurt Zouma - 4/10
Lost the ball too easily in a vulnerable position just before the penalty situation. He was also slow to press Pascal Gross before the second goal.
Thilo Kehrer - 4/10
It was the German's first start for West Ham and he did not show his best side in front of a packed London Stadium, as he gave away a foolish penalty in the first half and did not impose himself much on the rest of the game.
Aaron Cresswell - 5/10
Completely anonymous first half and did not impact his team's attacking play, like we know he can. He made some unnecessary fouls in dangerous areas and eventually got booked too.
Tomas Soucek - 5/10
Other than a headed attempt that was saved in the second half, the Czech found it difficult to control the game in midfield or create opportunities for his teammates.
Declan Rice - 6/10
Pings the ball around the pitch with great accuracy as always. But a worrying lack of forward, threatening passes. No significant impact as the Hammers desperately needed goals.
Pablo Fornals - 5/10
Had a good chance from 18 yards but his shot was straight at the Brighton goalie. Otherwise anonymous. Subbed off after 60 minutes.
Jarrod Bowen - 5/10
Bowen is a real threat when he can run with the ball towards goal. Unfortunately he only found himself in that situation a couple of times on Sunday. He had a great chance to play Michail Antonio through on goal but a poor pass stopped the attack.
Said Benrahma - 5/10
Had the game's first chance with a wide shot. Made some good runs with the ball down the flank but did not create enough attacking chances for himself or his team.
Michail Antonio - 6/10
Busy man. Antonio did well battling Brighton's three centrebacks. His duels and runs helped the Hammers push into Brighton's final third at times, but there was no end product. Antonio ended the game without a single shot.
Substitutes:
Gianluca Scamacca (62') - 5/10
Came on in the 60th minute and did not create the chances needed or, like Antonio, have a shot at goal.
Maxwel Cornet (75') - 5/10
The summer signing from Burnley got 15 minutes to make an impact and was not able to change to score.
Manuel Lanzini (75') - 6/10
He had some good combinations that god West Ham up the pitch.
Ben Johnson (75') - 6/10
The West Ham graduate came on for Coufal and looked solid.
Brighton
Robert Sanchez - 7/10
Not put to the test by West Ham until late in the game. The Spaniard makes two good, consecutive saves in the 83rd minute to keep a clean sheet for his team.
Joel Veltman - 6/10
The Dutch international had a fine game as one of Brighton's three centrebacks. No mistakes and safe on the ball.
Lewis Dunk - 6/10
Kept close to Antonio and battled well. Won some, lost some.
Adam Webster - 5/10
Had a shaky start as he lost possession a few times. Did not seem secure on the ball throughout.
Solly March - 6/10
Missed a great chance late in the second half to make it 3-0. Otherwise secure and at times inventive with the ball.
Alexis Mac Allister - 7/10
Scored Brighton's penalty goal. Worked hard in midfield and distributed the ball well.
Moises Caicedo - 7/10
The Ecuadorian was great on the ball, almost errorless. Did well to find his teammates further up the pitch.
Leandro Trossard - 7/10
Scored the second with a composed strike through on goal. Always seemed like something productive could happen when he had the ball.
Pascal Gross - 6/10
Anonymous first half but showed his skills with a beautiful flicked through-ball for the visitors' second goal.
Adam Lallana - 5/10
Work hard but had little impact on the game going forward. Off after 63 minutes.
Danny Welbeck - 6/10
Great run and drive with ball to get the penalty kick in the first half. Good job pushing West Ham back with his runs behind the lines.
Substitutes:
Pervis Estupinan (63') - 6/10
Great cross after coming on, which should have resulted in Brighton's third goal. Energetic performance.
Enock Mwepu (85') - N/A
Kaoru Mitoma (90') - N/A