The England striker tapped in Cristiano Ronaldo's low cross from three meters (yards) after only 56 seconds. But he was forced off the Old Trafford field with the injury to his leg about five minutes later.

"With a hamstring you are talking a minimum of three weeks," United manager Alex Ferguson said. "We hope it isn't any longer than that."

With a game in hand, the defending champions are two points behind Liverpool, which has 46. Chelsea, which dropped to third place with 42 points, played in the FA Cup and conceded an early goal at League One team Southend in a third-round replay before recovering to win 4-1.

In other replays, Hull beat Newcastle 1-0 and Crystal Palace edged Leicester 1-0. At Old Trafford, fans were expecting a rush of goals after Rooney scored his ninth goal of the season so quickly, but Wigan threatened like a team coming off the back of a four-match winning streak.

"Rooney gave us a great start," Ferguson said. "We should have put it to bed the amount of chances and penetration we had by halftime, but they made us work."

Rooney's departure provided Carlos Tevez with a chance to prove himself to Ferguson as talks drag on to secure a permanent deal at the end of the season. But after beating the offside trap and latching onto John O'Shea's header, the Argentina striker took the ball too far beyond Wigan goalkeeper Chris Kirkland.

Wigan's best chance came when the unmarked Paul Scharner headed into the side netting. Chelsea's match at Southend was initially called off due to the foggy conditions, but referee Chris Foy reversed his decision an hour before kick-off.

After conceding five goals from set pieces in their last three matches, Chelsea's players spent the aftermath of Sunday's 3-0 loss at Manchester United working on a new zonal marking system. But a third-tier side needed only 16 minutes to breach it, with Southend captain Adam Barrett leaping unchallenged to head Junior Stanislas' corner past Petr Cech.

As chants of "You're getting sacked in the morning" were directed at Chelsea manager Luis Felipe Scolari by the home fans, Cech threw his body at Alex Revell's header from point-blank range and Franck Moussa shot over from the rebound.

But in the last minute of the first half, Michael Ballack produced the equalizer that the dominant visitors had deserved.

There was confusion between Southend goalkeeper Steve Mildenhall and Peter Clarke when dealing with Jose Bosingwa's high ball and the half-clearance fell to Ballack to volley into the top corner.

Salomon Kalou spared Chelsea an embarrassing loss by scoring the second goal in the 60th after a fine individual move. The Ivory Coast winger cut inside Johnny Herd before slotting the ball through the legs of Barrett and into the far corner of Mildenhall's goal.