Nigel Reo-Coker answered Alan Curbishley's call to do his talking on the pitch by grabbing the winner in the West Ham manager's first game in charge.
Skipper Reo-Coker, who has suffered a slump in form this season and has been linked with a move from the club, scored the only goal at Upton Park against Barclays Premiership leaders Manchester United.
United's lead at the summit had been cut to two points following Chelsea's win earlier in the day, and they were denied by a polished performance from goalkeeper Robert Green.
Green kept the hosts in the game with a stunning save to deny Cristiano Ronaldo in the second half, and Reo-Coker's near-post finish meant a triumphant start to Curbishley's reign.
Curbishley, who grew up in nearby Canning Town, had promised to select his starting XI on what he had seen in training since his appointment on Wednesday.
As a result Carlos Tevez, the Argentina striker who has not broken his Hammers duck, was on the bench and there was no place for his compatriot Javier Mascherano in the squad.
Curbishley also stated he had not spoken to Reo-Coker about his role at the club, but the skipper weighed in with the goal that gives his side renewed hope as they battle against relegation.
Curbishley had not beaten United during his 15 years as Charlton boss, and the early signs were that the visitors were not in the mood to hand him a victory to complement the rapturous welcome he received before kick-off.
With Chelsea defeating Everton at Goodison Park earlier in the day, United knew they needed a win to keep the pressure on the champions.
Ryan Giggs had a shot blocked in the opening 30 seconds and Wayne Rooney volleyed over early on when Michael Carrick, the former Hammers midfielder, fed him the ball on the edge of the area, but the hosts weathered the early storm.
Half-chances went begging for United and the hosts almost snatched an early lead when Matthew Etherington was found in front of goal by Lee Bowyer with a cross from right, but the winger could not direct his header.
Marlon Harewood also fizzed a volley over the crossbar in the 17th minute as the hosts built a little bit momentum.
However, Hammers goalkeeper Green was forced to parry Louis Saha's low effort from the edge of the area after the France striker went on a run from the halfway line.
Green stopped Saha twice towards the end of the first half but none of the chances were as clear as the opportunity Bobby Zamora spurned just after the half-hour mark.
Jonathan Spector's long ball looped over Rio Ferdinand, Zamora held off the defender but Edwin van der Sar managed to claw his effort away.
United, who had full-back Gabriel Heinze booked in the first half, then went on the counter-attack but Green was equal to their effort on goal.
Ronaldo earned a free-kick three minutes into the second half and Green recovered after fumbling the 40-yard set-piece from the Portugal winger.
Ronaldo then came even closer. He was denied by a stunning save from Green in the 56th minute after he cut in from the left following a slack pass from Harewood which allowed Rooney to start an attack.
Paul Konchesky drilled an effort wide at the other end just before Zamora was replaced by Teddy Sheringham, a Champions League winner with United, in the 59th minute. Referee Phil Dowd then turned down two penalty appeals against Anton Ferdinand, the first for handball from Saha's cross and the second for a challenge on Nemanja Vidic.
Yossi Benayoun was brought on for the final 20 minutes, replacing Hayden Mullins.
Reo-Coker netted his winner with 15 minutes remaining, finishing at the near post after Harewood had held the ball up on the byline and squeezed his cross in.
Teams:
West Ham Green, Spector, Ferdinand, Collins, Konchesky,Bowyer, Reo-Coker, Mullins (Benayoun 71),Etherington (McCartney 77), Harewood, Zamora (Sheringham 59).
Subs Not Used: Carroll, Tevez.
Booked: Reo-Coker, Sheringham, Ferdinand.
Goals: Reo-Coker 75.
Man Utd Van der Sar, Neville, Ferdinand, Vidic,Heinze (Park 88), Ronaldo, Carrick (O'Shea 84), Scholes,Giggs (Solskjaer 73), Rooney, Saha.
Subs Not Used: Kuszczak, Silvestre.
Booked: Heinze, Vidic.
Att: 34,966
Ref: P Dowd (Staffordshire).
Reo-Coker made Man Utd pay for not taking their chances as he scored the winning and only goal in a lively encounter.
