Park pounces to sink Liverpool
United's tense 2-1 victory over Liverpool earlier on Sunday moved them on to 69 points with seven matches remaining, two points clear of Arsenal, the overnight leaders. Chelsea are third on 65 points, but have a match in hand over the leading pair.
The race for fourth place also intensified with Tottenham Hotspur remaining fourth on 55 points, two ahead of Manchester City who won 2-1 at Fulham on Sunday and have a match in hand on Spurs.
Liverpool's 10th defeat of the season saw them slip back to sixth on 51 points and their chances of securing fourth and a place in the Champions League preliminary round are fading fast.
United recovered from an early shock to win a scrappy game at Old Trafford where goals from Wayne Rooney and Park Ji-sung earned them a deserved victory.
Liverpool struck first in glorious spring sunshine when an unmarked Fernando Torres headed in Dirk Kuyt's cross after only five minutes but their lead was shortlived.
United drew level seven minutes later after Javier Mascherano conceded a penalty for a foul on Antonio Valencia and, although Rooney's spot-kick was saved by Pepe Reina, the England striker pounced on the rebound to score his 33rd United goal of the season.
Korean Park scored the winner when he converted Darren Fletcher's cross from the right with a brave diving header after 60 minutes.
"It wasn't a classic, but it was so intense, I am sure no-one went for a cup of tea watching it on television that's for sure," United manager Alex Ferguson told Sky Sports.
Liverpool boss Rafa Benitez later said the penalty had proved a turning point.
"One situation changed everything," Benitez told reporters.
"I've seen three replays and the last one was very suspicious, seeing the replay and how he fell to the ground. There is maybe a contact but the way he fell down -- strange."
The victory strengthened United's challenge to become the first English club to win four successive titles. It would be their 19th crown, one more than Liverpool.
Their quest was aided when Chelsea failed to capitalise on their superiority at Blackburn to complete a miserable few days for Carlo Ancelotti's side after they were knocked out of the Champions League by Inter Milan on Tuesday.
Chelsea grabbed the early initiative when Didier Drogba put them ahead after six minutes with his 22nd league goal of the season, but Rovers pulled level 20 minutes from time.
Chelsea failed to deal with a Michel Salgado cross which El-Hadji Diouf headed home at the far post to give Blackburn a share of the points, despite late and intense Chelsea pressure.