Frank Lampard thundered in a 21st-minute penalty to open the scoring for Jose Mourinho's side, with his second goal, eight minutes before full time, marking his fifth in as many appearances against his old club. Those two strikes sandwiched Oscar's 34th-minute effort as Chelsea claimed its first Premier League win in three matches.
Lampard's penalty came after Guy Demel's mistake let in Oscar, who was brought down by goalkeeper Jussi Jaaskelainen, before Oscar himself made it two with a low effort from the edge of the box. And Lampard doubled his tally late on, converting from the top of the penalty area after Jaaskelainen parried Eden Hazard's shot, leaving West Ham without a win in five league matches.
Both sides made one change from their previous outings a fortnight ago. Joey O'Brien replaced the injured Razvan Rat for the hosts, while John Obi Mikel came in for Willian in the Chelsea midfield.
After a scrappy start to the game, the visitors were gifted the lead midway through the half. Under no pressure, Demel's weak back pass toward Jaaskelainen was seized upon by Oscar, who went to ground under the goalkeeper's sliding challenge. Referee Chris Foy showed no hesitation in pointing to the spot.
Lampard stepped up and smashed the kick high into the roof of the net to end his longest run without a league goal for Chelsea.
Thirteen minutes later, Oscar tormented the hosts again. The Brazilian picked up Hazard's clever flick before driving forward and rolling the ball into the bottom left-hand corner from 20 yards.
Jaaskelainen produced a fine save to deny Samuel Eto'o three minutes before the break, flying high to his left to parry the Cameroon international's curling shot behind.
Chelsea started the second half strongly, Gary Cahill seeing his header cleared off the line by Mark Noble in the 52nd minute before Oscar turned Cesar Azpilicueta's cross wide four minutes later.
The hosts ought to have reduced the deficit in the 64th minute when substitute Mohamed Diame jinked past three defenders on the byline before his deflected cross ran to fellow replacement Modibo Maiga, who turned the ball a foot wide of the post from 6 yards.
As the game entered its final 10 minutes, Hazard tested Jasskelainen from an angle and the rebound fell perfectly to Lampard, who made no mistake with a first-time strike.
Demba Ba saw an injury-time goal chalked off for offside but the points were already in the bag for Chelsea, which moves up to third, while West Ham is just one place above the relegation zone.