Frank Lampard had been stuck on 199 goals for the last month but the England midfielder fittingly reached the landmark against his former club as he powered home a first half header to end a run of four scoreless matches.
The 34-year-old, who joined Chelsea from West Ham for £11 million in 2001, is just two goals away from equalling Bobby Tambling's all-time record for the west Londoners, yet remarkably he could still leave the club on a free transfer at the end of the season.
More significantly for Chelsea interim manager Rafael Benitez, Lampard's 14th club goal of the season helped secure a priceless win in the battle for a top four finish.
Eden Hazard added Chelsea's second goal early in the second half and that was enough to ensure Benitez's team move one point above Tottenham, beaten by Fulham earlier on Sunday, and remain five points clear of fifth placed Arsenal.
West Ham have lost five of their last seven league games and Sam Allardyce's men are now only six points above the relegation zone.
Benitez opted to restore Demba Ba to the starting line-up in place of Fernando Torres, even though the Spaniard had contributed a rare goal to the midweek Europa League win over Steaua Bucharest, and the Senegal striker was immediately at the centre of the action.
Lampard split the West Ham defence with a superb pass that sent Ba through on goal, only for the forward to scuff his shot well wide.
West Ham under Allardyce are unapologetic disciples of the long-ball game and they tried to over-power Chelsea with an early aerial barrage that ended with James Collins lashing a volley just over.
But West Ham's defence was exposed too often and Chelsea took full advantage to open the scoring in the 19th minute.
Hazard drove in a long-range shot that goalkeeper Jussi Jaaskelainen pushed out to Victor Moses and the Nigerian's cross was only half-cleared by Collins back to Hazard.
Given too much time and space by the hesitant Hammers rearguard, the Belgian playmaker lofted a fine cross towards Lampard and he rose unmarked to guide his header past Jaaskelainen.
Lampard celebrated in front of the West Ham supporters and was joined by team-mates including substitute John Terry, who had already angered the visiting fans by warming up close to them moments earlier, with both players targeted by missiles thrown from the away end.
Allardyce's team thought they had hit back immediately when Andy Carroll fired home after Matt Jarvis stretched to hook over a cross from the touchline, but the goal was ruled out for a foul on David Luiz.
Chelsea were causing constant problems for West Ham's leaden-footed defence and Moses and Luiz had shots saved from long-range.
Ba was guilty of more poor finishing when he shot too close to Jaaskelainen and then dragged a second chance wide.
But Chelsea delivered the knockout blow in the 50th minute with a sublime move started and finished by Hazard.
When he flicked a pass towards Juan Mata, Hazard didn't stop to admire his handiwork. Instead he sprinted onto the return pass from Mata and surged into the penalty area before deceiving two West Ham defenders with a clever feint, opening space to drive a powerful shot past Jaaskelainen.
Lampard should have moved even closer to Tambling's record in the closing moments when Oscar found him 10 yards from goal, but his strike sailed high over the bar.