The 1-1 draw was music to the ears of Manchester United, who now seem uncatchable, no matter what the outcome when they visit Stamford Bridge in a week and a half.
Chelsea lost the war in midfield, with Frank Lampard dropping out of the squad at the 11th hour for what were described as personal family reasons.
The first half was a turgid affair, with Chelsea failing to find any fluidity and Wigan continually frustrating their opponents. French winger Florent Malouda was a virtual spectator, as he and some of his Chelsea team-mates failed to make any mark on proceedings.
Fan power eventually persuaded Chelsea manager Avram Grant to bring on Joe Cole at the start of the second half, transforming a game which had lumbered along for 45 relatively uneventful minutes.
Wigan matched Chelsea in attack in the first half with Petr Cech, now looking like the first victim of the monster in a horror film, wearing a chinguard as well as his trademark skull cap, making several crucial saves.
At the other end, Chris Kirkland also made a string of brilliant saves, crucially denying Nocolas Anelka, clawing the ball out of the goal as he fell backwards into the net in the 27th minute.
Michael Essien capitalised on Cole's hard work ten minutes after the restart, slamming the ball into the top left-hand corner of the net after Anelka had teed him up.
Everything looked as if it was proceeding towards another 1-0 home victory until Wiganstruck from a breakaway attack two minutes into the three minutes of stoppage time that referee Andre Marriner had decreed be added.
Heskey met a superb curling Jason Koumas cross and beat Cech at the far post.
In a desperate last-gasp reshuffle, Grant brought on Andriy Shevchenko to a chorus from the fans of 'you don't know what you're doing' and the final whistle only brought more boos from sections of the home fans.