United came to Ewood Park needing a point to win the Premier League crown and for the first 20 minutes the party was underway as if they had already achieved manager Sir Alex Ferguson's famous vow to knock arch-rivals Liverpool "off their perch."
When Brett Emerton put Blackburn ahead, however, the United fans hastily shoved their celebratory banners in their pockets, covered up their specially made '19' T-shirts and fell quiet.
They looked on nervously until 17 minutes from time when Rooney's spot-kick restarted the celebrations which began in earnest when the final whistle went and the stadium erupted.
United's substitutes charged on to the pitch with Ferguson, hugging their team mates as they jumped up and down with a makeshift trophy in front of thousands of travelling fans.
SPECIAL OCCASION
The supporters lingered in the stadium and Ferguson marked the occasion by attending a post-match news conference for the first time this season.
"That's the important thing, being the most successful and hopefully keep it going for a long time. It's a great achievement," he said, adding that he was not even sure that he had ever uttered the well-documented "perch" statement.
Fans had picked the phrase up from somewhere, nevertheless, and it was the basis of most of the mottos on the United banners, some of which declared "Knocked off your perch 19-18" or "Sat on our perch."
Having seen Nani crack the crossbar and shoot wide with just a few minutes on the clock, the United fans may have been expecting a rout like the 7-1 thrashing their team dished out to Blackburn earlier this season.
Instead any hand-rubbing was about keeping warm in a windy open stand on a chilly day in the Lancashire town as relegation-threatened Blackburn went about trying to poop the party.
The young boy who had made himself a double-sided cardboard cutout of a trophy with '19' on one side and 'Champions League" on the other will get the chance to use it again when United travel to Wembley to face Barcelona on May 28.
Jubilant fans prepared to make the short journey back to Manchester to get the champagne out and the message to Liverpool was clear.
"Look on and admire," Liz Clancy, wearing a "Champions 19 Times" scarf, told Reuters when asked what she wanted to say to the club's arch-rivals. "And please shut up."
