Ricardo Vaz Te hit a hat-trick as West Ham maintained their automatic promotion hopes by thrashing a Brighton side whose play-off hopes were dented.
The Hammers, now three points behind second-placed Southampton, took the lead through Vaz Te's early strike.
A Vaz Te header and Kevin Nolan tap-in then put West Ham 3-0 up in 11 minutes.
A bicycle kick from Vaz Te, Carlton Cole's deflected shot off team-mate Henri Lansbury and a Gary Dicker own goal completed the Upton Park rout.
The victory was West Ham's first in eight games at home, while Brighton are five points adrift of the play-off places.
Southampton had been beaten by top-of-the-table Reading on Friday and West Ham made a blistering start as they attempted to capitalise.
Vaz Te broke the deadlock before quickly adding a second as he took his tally to seven goals in the last five games.
Nolan added to Brighton's woes and it could have been worse for the visitors when a deflected Lansbury shot came off the crossbar.
Brighton had a rare chance when Gordon Greer saw a header saved by keeper Robert Green but Gus Poyet's side did not help their cause by giving away possession on a regular basis.
West Ham were a far cry from the team that had drawn six and lost one at Upton Park during the end-of-season run-in as they carried an air of confidence and creativity.
Vaz Te's acrobatic goal in the second half completed his hat-trick before Cole's shot came off his team-mate Lansbury to add to the Hammers lead.
Brighton's misery was compounded when their midfielder Dicker put a Mark Noble corner into his own goal as the Hammers also reduced the goal difference gap on Southampton to three.