Sir Alex Ferguson, United's manager, had claimed he would be on the golf course instead of watching the match and he missed a hard fought contest.
Chelsea have been running on empty for weeks as the strain of their quadruple bid took its toll, but they deserved credit for their effort here.
Mourinho had been forced to field a below-strength side as Ashley Cole, who would have been returning to Arsenal for the first time since his acrimonious transfer, was ruled out with an injury, as were Didier Drogba and Andriy Shevchenko.
William Gallas came close to opening the scoring early on when he was unable to turn in Cesc Fabregas' free-kick.
But the game only really came to life in the 43rd minute after a piece of slap-stick defending from Boulahrouz.
The Dutch defender has been used sparingly by Mourinho and it was easy to see why as he misjudged the bounce from Adebayor's flick and then allowed Julio Baptista to muscle him off the ball before sending him sprawling with a rash challenge.
Alan Wiley awarded the penalty and wasted no time sending off Boulahrouz before Gilberto confidently sent Cech the wrong way from the spot to edge United closer to the title.
Trailing the Gunners, Chelsea summoned up the energy for one last desperate assault in the closing stages and were rewarded in the 70th minute.
Shaun Wright-Phillips whipped in a superb cross from the right and Essien dived in to glance a header into the far corner.
Cole had an effort ruled out for offside and Essien was close to a second as the visitors went down fighting.
Lampard could have won it in the last moments but shot wide and Jens Lehmann made a brilliant stop to deny Salomon Kalou.
At the final whistle Chelsea had made United sweat to the last but they couldn't stop Ferguson's men replacing them as kings of English football.
After a soap opera of a season at Stamford Bridge, the Blues had finally given up their crown, but Mourinho rightly asked Chelsea's fans to salute his players at full time for coming so close in every competition.
However, the Portuguese coach faces a tough task to revitalise the squad in time for the FA Cup final against United on May 19.