An injury-time header from Phil Jagielka gave Sheffield United a dramatic draw at Bramall Lane.
The home side trailed 3-1 with 20 minutes left but fought back to earn a point.
Paul Peschisolido put Sheffield United ahead in the fifth minute before Michael Carrick, Jon Harley and Marlon Harewood responded for the Hammers.
A Paul Shaw strike in the 71st minute was followed by a Michael Tonge penalty miss, before Jagielka finally levelled.
West Ham began with a new-look defence as recent arrivals Andy Melville and Harley made their debuts, and Stephen Bywater replaced David James in goal.
And the Blades took full advantage when Peschisolido opened the scoring from close range after a cross from Nick Montgomery.
But the Hammers then took control and dominated the rest of the opening period.
David Connolly sent Carrick clean through in the 19th minute and the midfielder calmly slotted into the corner.
Harley then produced one of the goals of the season on his debut, finding the top corner from 25 yards out.
And when Matthew Etherington's cross was converted by Harewood there looked to be only one winner.
But West Ham have been fragile when in front all season and it proved to be the case again as the home side threatened to overrun them at times in the second half.
However, it was not until the 73rd minute that Shaw cut the deficit, despite claims from West Ham that Anton Ferdinand was fouled in the build-up.
The young defender was clearly shaken and moments later gave away a penalty with a clumsy challenge on Peschisolido.
Bywater was set to be the Hammers' hero when he saved Tonge's spot-kick but the young 'keeper was at fault for the final goal.
Etherington was twice through on goal and could have wrapped up the match for West Ham but could not finish.
Tonge's late corner then left Bywater stranded and Jagielka's looping header found the back of the net to send the home fans wild.
Sheff Utd: Kenny, Phil Jagielka, Kozluk, Morgan, Page, McCall,
Montgomery, Tonge, Lester, Peschisolido, Allison. Subs: Wright,
Whitlow, Shaw, Rankine, Sturridge.
West Ham: Bywater, Harley, Ferdinand, Dailly, Melville,
Carrick, Horlock, Mullins, Etherington, Connolly, Harewood.
Subs: Shaaban, Stockdale, Deane, Mellor, Cohen.
Referee: P Durkin (Dorset).