Centre back Phil Jagielka netted a stoppage-time equaliser to snatch a vital point for Neil Warnock's battling promotion favourites.
The England Under-21 defender struck with seconds to go as the Blades fought their way back after West Ham had surged into a 3-1 lead.
Sheffield United had swept ahead in the fifth minute, midfielder Nick Montgomery finding space on the right flank to pump in a low cross and Paul Peschisolido lunged at the ball sticking out a foot to steer it wide of Stephen Bywater and into the far corner of the net.
Michael Carrick curled a free-kick into the area that ended with the ball being hacked clear by Jagielka before West Ham equalised in the 19th minute.
David Connolly, deep in Sheffield United territory, fed Carrick who slipped past Jack Lester before beating the advancing Paddy Kenny from 12 yards.
But the Hammers were in control four minutes later as full-back Jon Harley unleashed a 20-yard left-foot shot, the ball flying into the top right-hand corner with Kenny rooted to the spot.
Marlon Harewood, a Â£500,000 buy from Nottingham Forest, grabbed West Ham's third in the 37th minute. Matthew Etherington was the provider with a precise cross to the far post and as full-back Rob Kozluk hesitated the lanky striker pounced, volleying the ball over the line from close range.
Veteran midfielder Stuart McCall had a shot deflected before he set up the Blades' second in the 73rd minute picking out substitute Paul Shaw who beat Bywater with a low angled drive from just inside the area.
Sheffield United were handed a chance to draw level three minutes later, when Anton Ferdinand bundled Peschisolido over in the area.
Tonge's penalty kick had power but Bywater produced a stunning save leaping to his right to push the ball away.
Etherington should have snatched a fourth six minutes from time when he burst through unmarked but was foiled by Kenny as he darted off his line.
Bywater pulled off another stunning stop in the dying minutes to keep out substitute Dean Sturriudge before Jagielka had the last word.