Manchester United squandered a chance to temporarily regain the Premier League leadership when it was held 0-0 by Blackburn on Sunday to stay behind Chelsea in the title race.
A victory would have put United a point ahead of Chelsea but Antonio Valencia and Dimitar Berbatov both missed chances at Ewood Park.
Chelsea, which now leads the league by one point, has the chance to go four clear of United by beating Bolton at home on Tuesday.
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"It’s a blow, there’s no question about that, and it makes it really difficult to win the league now," said United manager Alex Ferguson, whose team is trying to become the first to win the league title four times in a row.
"That’s a fantastic result for (Chelsea). They will be really delighted at that and they have a home game against Bolton on Tuesday. They will be expected to win that of course. We needed to win today. We are a point behind Chelsea and they have a game in hand and that would take it to four points and it’s a big gap."
Without 34-goal Wayne Rooney, who is sidelined with an ankle injury, United failed to dominate a mid-standings Blackburn side and its first clear chance did not come until just before halftime when Valencia broke clear only for Blackburn goalkeeper Paul Robinson to block his shot.
Berbatov had a good chance in the 80th minute when he was unmarked 15 meters (yards) out but shot straight at the ‘keeper. Three minutes later, the Bulgaria striker, whose inconsistent form has made him unpopular with many of the United fans, fired wide from the edge of the area.
Deep into injury time, a half-chance fell to United rightback Gary Neville but he pulled his shot wide with his weaker left foot.
Manchester City strengthened its hold on fourth place with a 5-1 victory over Birmingham.
After Carlos Tevez had stroked home a 38th-minute penalty, Nedum Onuoha and Emmanuel Adebayor scored two goals each to move City on to 62 points from 33 games. Fifth-place Tottenham, which faces Portsmouth in Sunday’s FA Cup semifinal, has 58 from 32.
Without injured striker Fernando Torres, Liverpool was held 0-0 at home by Fulham to lose more ground on City in the race for fourth. Rafa Benitez’s sixth-place team now has 56 points from 34 games, with Aston Villa next on 54 from 32.
Wolves edged closer to safety with a 0-0 draw at home to mid-table Stoke and is now six points above the relegation zone with four games still to play.