Chelsea were a shadow of the side that has built a nine-point lead in the Premier League during Tuesday's 1-0 Champions League defeat by Real Betis.

They showed little application in the first half, giving the ball away far too often, and went behind to a goal from substitute Dani in the 28th minute.

Chelsea improved in the second half against an inspired Betis and were unlucky not to equalise when a shot by midfielder Michael Essien hit both posts without crossing the line.

However, Mourinho acknowledged Chelsea did not deserve to avoid their first defeat inside regulation time this season.

"It was the worst performance since I arrived," Mourinho said. "I've been here for 15 months, perhaps 80 matches at Chelsea, and this was the worst performance.

"The first half was too bad to be true. Maybe the players thought it was a knockout game and we were 4-0 up.

"The attitude was too relaxed for a game when we're playing for points."

European champions Liverpool lead Group G with 10 points from four games after their 3-0 defeat of Anderlecht, and Chelsea have seven points, one ahead of Betis.

Chelsea's rampaging start to the season has been checked in the past 10 days with a 1-1 draw against Everton, a defeat on penalties in the League Cup against Charlton Athletic and now defeat by Betis.

Mourinho's bombastic rhetoric has shown few signs of cooling despite the comparative setbacks but the Portuguese acknowledges it may now be time to lend an ear to others' opinions.

"This is the kind of game I want to analyse by full communication. I want to listen to my players," Mourinho said.

"The more they speak, the more I listen. We need that communication because the performance was not acceptable."

Whatever the Chelsea players say, they will be left in no doubt that more application and grit will be needed on Sunday against United, one of the biggest games of the domestic season.

The match at Old Trafford is seen by the media as a possible watershed in the career of United manager Alex Ferguson because defeat would end the home side's title aspirations after just 11 games. United are 13 points adrift of their London rivals.