Manchester: Manchester United manager Alex Ferguson was left nonplussed after a linesman failed to flag for an offside against Didier Drogba which gave Chelsea the edge in the race for the Premier League title.

United, trailing 0-1, were having the lion’s share of the chances midway through the second half of a fraught match at Old Trafford on Saturday when Drogba made what might prove the decisive intervention in the race for the crown.

The Ivory Coast international was in an offside position when he received the ball from Saloman Kalou before smashing home superbly from an angle past Edwin van der Sar to give Chelsea a 2-0 advantage. They held on for a 2-1 win.

“What I can’t understand is the linesman’s directly in front of it,” said an exasperated Ferguson after watching his side slip two points behind their London rivals.

“He has no one near him and he gets it wrong. A game of that magnitude, you really need quality officials and we didn’t get them today. It was a poor, poor performance.”

Ferguson refused to be drawn on referee Mike Dean, whose appointnment for the match had caused debate ahead of the game.

“I don’t know about that. I’m not going into that. When I saw it was Mike Dean, I did worry, I must admit,” he told the club’s website.