Carlo Ancelotti admits Chelsea will have to improve quickly if it is to avoid a Champions League exit at Manchester United on Tuesday.

Ancelotti's side travel to Old Trafford for the quarterfinal second leg trailing 1-0 after Wayne Rooney's strike in the first leg at Stamford Bridge.

Chelsea returned to winning ways with a narrow 1-0 home victory over bottom club Wigan on Saturday, but the Blues were once again well below their best.

Chelsea manager Ancelotti conceded a similar performance would spell disappointment against Sir Alex Ferguson's side.

"It was positive to win. It was not easy," Ancelotti said.

"The first was not good, the second half was better, good spirit and fighting, but in the end we won which is the most important thing.

"We have to play better on Tuesday. To win there we have to play at 100 percent."

Ancelotti and his players can point to their success in winning at Old Trafford in the latter stages of last season, a victory that proved decisive in their bid to pip United in the title race.

But last year Chelsea was in outstanding scoring form and Ancelotti acknowledges his side faces more testing problems this time around.

"Obviously we have more difficulty compared to last season," he said. "Last season we scored a lot of goals and we have difficulties to score now.

"We created a lot of opportunities today when we were 1-0 up, we were not able to do this."

Florent Malouda scored the decisive goal against Wigan in the 67th minute but Fernando Torres again drew a blank during a 31-minuute substitute appearance.

Ancelotti refused to reveal whether the Spain striker would start against United, but he admitted he was willing Torres to score when he was twice denied by late saves from Wigan keeper Ali Al Habsi.