The result left Chelsea with 32 points from 16 matches, four behind second-place Manchester United and six behind longtime leader City.
"It is a disappointing result," Chelsea manager Andre Villas-Boas said.
"It was a hard-fought game with many chances on both sides, maybe more from Wigan. They fought hard to get the result here. I think Wigan had the momentum, and the crowd was behind them, and they got the goal they deserved; 1-1 was a fair result."
Defending champion United could go to top of the Premier League for the first time since mid-October if they win at Queens Park Rangers today and local rival Manchester City lose to visiting Arsenal. Sunderland are at fourth-place Tottenham and Liverpool are at Aston Villa in today's other matches.
The draw left Wigan in the relegation zone with Blackburn and Bolton, who remained anchored to the bottom of the Premier League after a 2-0 loss at Fulham.
Two weeks after becoming the most prolific American scorer in England's top division, Fulham forward Clint Dempsey scored his 38th Premier League goal and fifth this season with a 32nd-minute header from Bryan Ruiz's cross.
Dempsey has eight goals in all competitions this season and three in his last four games.
"He scores so many goals," Fulham manager Martin Jol said. "I'm very happy with him."
Costa Rica forward Ruiz chipped goalkeeper Jussi Jaaskelainen two minutes later as Fulham left Bolton with only nine points from 16 games, one fewer than a Blackburn side that lost 2-1 against visiting West Bromwich Albion.
Peter Odemwingie scored West Brom's winning goal with just a minute remaining.
Wolverhampton Wanderers are still just one place and one point above the relegation zone after conceding two second-half goals to lose 2-1 against Stoke. Wolves led through a 17th-minute penalty, but Kevin Doyle's own-goal and the 99th league goal of Peter Crouch's career clinched Stoke's fourth straight Premier League win.
Stoke are now just three points behind Newcastle, who spent three months in the top four but are now without a win in five matches after drawing 0-0 with visiting Swansea.
In the League Championship, West Ham beat Barnsley 1-0 to go level on points with longtime leader Southampton. AP