With just two games remaining United have all but got their hands on the Premier League trophy and if the Reds had the perfect start Chelsea were left with a mountain to climb after going two down by the 23rd minute.
For a team with the best defensive record in the top flight the Blues looked vulnerable at the back.
With Antonio Valencia and Park in sparkling form Chelsea struggled to get a foothold in the game even though Salomon Kalou had a couple of decent chances, by the time the Blues had settled down they were chasing the game.
Chelsea showed more urgency after the break as United lost their dominance and with 21 minutes remaining Frank Lampard pulled a goal back. Ramires crossed and Alex’s knock down was prodded home from close range.
Fernando Torres came on as a substitute but made little impact.
United have now collected 52 points out of a possible 54 on home soil this season, and are unbeaten at Old Trafford since April 2010 having endured four minutes of stoppage time the final whistle was greeted as if Sir Alex Ferguson had already won a record 19th league title.
But in reality Manchester United now need just one point at Blackburn on Saturday to be crowned champions.
Referee: Howard Webb
Venue: Old Trafford
Man Utd scorers: Hernandez 1, Vidic 23
Chelsea scorers: Lampard 68
01 Van der Sar
20 Fabio Da Silva (Smalling 88)
22 O'Shea (Evans 46)
11 Giggs (yellow card)
13 Park Ji-Sung
10 Rooney (yellow card)
02 Ivanovic (yellow card)
03 A Cole
04 David Luiz (Alex 46)
05 Essien (yellow card)
12 Mikel (Ramires 46 (yellow card)
11 Drogba (yellow card)
21 Kalou (Torres 61)