A 93rd-minute strike from Juan Mata was enough to sink a Wigan side who had been equal to Chelsea for large parts of the match.
Chelsea struggled to break Wigans resilient defence down, and both of their goals came in dubious fashion, while Diame scored a cracking equaliser for the visitors.
With seven changes made for this clash, one eye must have been on Mondays tie with Fulham, which showed, as the fluency in Chelseas play was missing.
The game took a while to get going, Cahill and Figueroa tested opposing keepers from range, but no side could find that killer pass. Didier Drogba thought he had scored on his return, as his strike somehow ended up the wrong side of the post, with Al-Habsi well beaten.
The Wigan ‘keeper had to meet the Ivorians next effort though, as his close-range header was heading into the corner, but was well stopped. That was about it for the first-half action, and the second period started off in the same vein, with Drogba again looking frustrated, as Al-Habsi was using any part of his body to deny the big man.
Wigan had so far held Chelsea superbly, but we’re finally picked apart, albeit in cruel fashion. A poor free-kick was cleared straight to Meireles, who whipped a second ball into the box, leaving Ivanovic to stab home, leaving the away side perplexed as to why a flag had not been raised.
The protests were helpless, and when many teams could have simple gone to rot, Wigan held themselves up, and attempted to get back level, and continue their recent good form.
With Chelsea now on the back foot, Di Santo pounced on an effort, only to see the scorer become saviour as Ivanovic cleared from his goalmouth. But, the home side couldn’t hold out for long, Diame had only been on for 10 minutes before he crashed home an effort from outside the area, to give the away side a justified equaliser.
In a season where no game is a formality, Chelsea continued to press a valuable winner, one that would put them back ahead of Newcastle, and within a win of third, Juan Mata became saviour, as he has done many times this season.
Fernando Torres, who had started on the bench, connected fantastically with a volley, before seeing the shot crash off the woodwork. However, the rebound fell delightfully for fellow Spaniard Juan Mata, who turned the ball into the net, sending Stamford Bridge into a relieved cheer.
The win puts more pressure on Arsenal, who face Manchester City on Sunday, knowing that a win could put them two points further away from Spurs, who could only draw today.
Chelsea are next in action on Monday 9th April, when they play Fulham at Craven Cottage.
By Brad Smith