All had seemed so rosy for the home side when Neil Roberts gave the Latics a 33rd minute lead with a close-range volley, and with results elsewhere going in the home side's favour it seemed a place in the play-offs was there for the taking.
The home side had to win and hope that either Palace or Ipswich dropped points but there were no nerves among the ranks of either the players or the 21,000 crowd as Wigan set about their illustrious opponents.
West Ham United keeper Stephen Bywater made two cracking saves to keep his side in the hunt in the first half while Wigan keeper John Filan produced a top-notch effort to keep out a close-range Bobby Zamora header.
The Hammers upped the tempo after the break but it seemed Wigan would hang on until the dying seconds when substitute Deane rose high to head Michael Carrick's free-kick into the net and break Wigan's hearts.