Sheffield United secured a priceless three points at the expense of relegation rivals West Ham.
Sheff Utd boss Neil Warnock celebrates a crucial win
Michael Tonge opened the scoring six minutes before the interval with an unstoppable 20-yard free-kick.
And Phil Jagielka headed the second in the 68th minute after Carlos Tevez wasted West Ham's best chance, shooting over from only 10 yards.
Jon Stead made sure the Blades' relegation fears eased with another long-range strike 12 minutes from time.
The win opens up a vital five-point gap between Sheffield United and West Ham and ended the visitors' hopes of a fourth successive win.
The team line-ups reflected recent form, with Sheffield United making four changes and West Ham content to name the side that won at Arsenal.
And the opening half was wracked with tension and short on quality, inevitably given the stakes.
Tevez curled a shot over the bar from 12 yards after creating an opening, before Sheffield United's Colin Kazim-Richards wasted a glorious opportunity.
He volleyed over wildly at the far post after Keith Gillespie's cross had evaded a succession of West Ham defenders.
The Blades broke the deadlock six minutes before half-time, Tonge powering an unstoppable free-kick high past Robert Green after Anton Ferdinand had fouled Christian Nade.
West Ham, inspired by Tevez, came out after the break with real intent as they went in search of an equaliser.
Mark Noble surged into the box, only to be denied by a brave tackle from Claude Davis, who was injured in the process and had to be replaced by Chris Morgan.
Lucas Neill was left holding his head in anguish after he was thwarted by a brilliant save from Paddy Kenny low to his right.
And on the hour, Tevez wasted West Ham's best opportunity, cutting in cleverly only to shoot over the top from 10 yards.
It was a costly miss, with Sheffield United crucially doubling their advantage after 68 minutes.
Jagielka met Gillespie's corner with a firm downward header that beat Green and flew in at an unguarded post.
And Stead wrapped up a vital victory with a brilliant solo effort 12 minutes from time.
It was all the striker's own work as the chased a ball into the right-hand channel before cutting in and drilling a 20-yard effort low past Green.
Sheffield United manager Neil Warnock:
"We knew it was an important game.
"I don't think there was anything significant in the result other than we showed we are still very much in it after people had written us off over the last few weeks.
"I think the media have presumed both West Ham and Charlton would finish above us. But we have brought other teams into it now, which we wanted to do, and I don't think anybody can say who is safe and who is not.
"But we have given ourselves a fighting chance. We won as a team and we thoroughly deserved it. I thought we looked a Premiership side out there today."
West Ham manager Alan Curbishley:
"The vital games we have had since I came to the club we have lost such as against Charlton, Watford and here, while we also dropped points to Fulham.
"They are big games. We have not done enough against the teams around us. That's been our big problem. Sheffield United have clawed away from us now, but there's still a long way to go, and I don't think they will think they are safe."
Sheff Utd: Kenny, Geary, Jagielka, Davis (Morgan 56), Armstrong, Gillespie, Tonge, Montgomery, Kazim-Richards (Webber 83), Nade (Alan Quinn 61), Stead.
Subs Not Used: Shelton, Kozluk. Booked: Kazim-Richards, Jagielka.
Goals: Tonge 39, Jagielka 68, Stead 78.
West Ham: Green, Neill, Ferdinand, Collins, McCartney, Noble (Blanco 73), Reo-Coker, Bowyer (Mullins 65), Etherington (Boa Morte 65), Zamora, Tevez.
Subs Not Used: Walker, Spector.
Booked: Bowyer, Ferdinand, Tevez.
Ref: S Bennett (Kent).