West Ham are within touching distance of Premier League safety after digging deep to finally summon an iron-willed performance that simply overwhelmed feeble Leicester.
Desire and intensity - not words always associated with the Londoners' efforts this season - hallmarked the display of David Moyes' men, who truly rose to the demands of the occasion.
Defeat would have left West Ham vulnerable, with pressure heaped on their final two matches, against Manchester United and former manager Sam Allardyce's Everton, both at the London Stadium.
A close-range finish from Joao Mario and a magnificently struck volley by captain Mark Noble crowned a compelling all-round display in which defender Angelo Ogbonna and midfield power unit Cheikhou Kouyate were outstanding.
It was, however, another wretched afternoon for Leicester manager Claude Puel. Given a vote of confidence by the club owners 24 hours earlier, this was a tame surrender. Leicester have won just four times in 19 league matches under Puel and home supporters gave full vent to their disgust at the final whistle.
West Ham hardly looked like a side arriving on the back of successive 4-1 drubbings in a lively opening in which Marko Arnautovic twice caused panic down Leicester's left flank before inadvertently deflecting team-mate Manuel Lanzini's on-target drive away from danger in the 10th minute.
The Londoners set about their task in determined manner, industrious in midfield and quick to adopt a solid defensive shape when Leicester had possession in the visitors' territory.
Bright on the break, too, and after two near-misses, West Ham deservedly moved in front in the 33rd minute. Arnautovic had twice gone close, shooting at Leicester goalkeeper Ben Hamer, then hitting the crossbar, before turning provider.
Arthur Masuaku tore down the left, his deep cross being pulled back by Arnautovic for Mario to stroke in from close range. They should have been further clear by the interval, Lanzini rippling the side-netting as West Ham continued to dominate.
It was just two years ago, almost to the day, that Leicester collected the Premier League champions trophy in front of an ecstatic King Power crowd and proceeded to demolish Everton 3-1. How times change, the happy reign of Claudio Ranieri replaced by austere, increasingly troubled times under Puel.
Jeered off at half-time, Leicester tried to remedy the situation after the break. West Ham were in trouble immediately, Aaron Cresswell guiding the ball with his arm as he slipped under pressure from Jamie Vardy and receiving a yellow card. But it was just about the only moment of concern for the visitors.
West Ham's work-rate was typified on the hour when home dangerman Riyad Mahrez wriggled free in the visitors' penalty area but was instantly swamped by three defenders.
Terrace discontent was again evident when Puel made a double switch, Kelechi Iheanacho and Demarai Gray replacing Hamza Choudhury and Fousseni Diabate. "You don't know what you're doing," was the indictment of the increasingly frustrated home supporters.
It was the perfect time for West Ham to strike and three minutes later they had doubled their lead. Leicester only partially cleared a free-kick and there was Noble to flash a 20-yard screamer beyond Hamer. There was still almost half an hour to play but Leicester were beyond salvation.