United's defeat by Arsenal and Chelsea's win over Tottenham Hotspur over the weekend have shaken up the title race with Sir Alex Ferguson's side only three points ahead of the champions who travel to Old Trafford on Sunday.
A Frank Lampard goal for Chelsea which television replays showed had not completely crossed the line and a United appeal for a penalty for Gael Clichy's trip on Michael Owen have led to Ferguson voicing fresh concern over refereeing.
"They (Chelsea) got great decisions for them (on Saturday) and they seem to get these decisions at the moment," said Ferguson, who has already served a five-match touchline ban this season for criticising referees.
"They got one to win the league last season at Old Trafford," he added, referring to Didier Drogba scoring from an offside position. "So that's a worry. You go into a game worrying about these things."
Victory at Old Trafford would put Chelsea top on goal difference, an almost unimaginable situation for the most ardent Blues fan two months ago when they trailed United by 15 points.
Chelsea benefit from a week's rest before the game, while United divert thoughts to Wednesday's Champions League semi-final second leg against Schalke 04 where Ferguson must field a strong enough side to defend a 2-0 lead while keeping his top players fresh.
"They're two massive games," Ferguson, who has said he will make changes for the midweek game, told MUTV.
DECISIVE GAME
While Ferguson is counting on United's imperious home form to hold up, Chelsea need little reminder that they were the last team to win at Old Trafford more than a year ago.
"As we showed last year by going to Old Trafford and winning a decisive game in the Premier League, there's no reason why we can't go there and win again," local media quoted Chelsea captain John Terry as saying.
"There's no bigger spur than going to Old Trafford and winning to put ourselves right in the frame for bringing the Premier League trophy back to the Bridge."
Ferguson received his touchline ban for saying he "feared the worst" when he saw Martin Atkinson was refereeing his side's match at Chelsea in March which ended in victory for the London side and a remarkable turnaround in their fortunes.
Since that 2-1 win, Chelsea have dropped only two points and they are also unbeaten in the league for 10 games.
While their cause was helped by the controversial Lampard goal, United have not been without their own lucky escapes as defender Nemanja Vidic's hand ball was missed on Sunday when the Serb deflected Theo Walcott's dangerous cross for a corner.
United defender Patrice Evra refused to dwell on refereeing, saying the main problem against Arsenal was his team's below-par performance and that as long as they can rediscover their pace and creativity they had nothing to worry about.
"We just need to play the Man United way," he told MUTV.
"We have our destiny in our hands. We have a massive game against Chelsea. If we w
