United, trailing 1-0, 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.
NEWS:Chelsea triumph at Old Trafford
"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. Plenty of people are criticising him but I'm not going to go down that road," he told the club's website.
Ferguson conceded that Chelsea were now favourites to win the title for the first time since 2006 after Carlo Ancelotti achieved the Premier League double over Ferguson in his first season in charge at Stamford Bridge.
"Chelsea are in the driving seat now - there's no question about that," added Ferguson.
"They're two points ahead of us with five games left. They also have a better goal difference than us.
"I'm sure we'll respond. But we can win our next five games and not win it because Chelsea can win their five and win the league."
Ancelotti told his players, who still have tough matches away to Tottenham and Liverpool, not to get carried away.
"Nothing has been decided," said the Italian. "We have to stay focused. We are happy to win here because it's important for our confidence. But nothing has been decided.
"We've obviously now got more possibility than Manchester United of winning the title but there are still five games to play.
"What did I think of the referee's performance? I have never spoken about the referee during the season and I don't want to speak now."
How United must have wished Wayne Rooney had been on the pitch instead of watching in one of Old Trafford's executive boxes nursing an ankle injury.
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