Sir Alex Ferguson suffered the ignominy of watching his Manchester United side lose to basement club Blackburn on his 70th birthday.
Yakubu gave Rovers the lead from the spot after Dimitar Berbatov had pulled down defender Chris Samba.
The Nigerian made it 2-0 when he made the most of slack defending to thrash in, before Berbatov brought United back into the match with a header and shot.
But Grant Hanley spoilt the day for Ferguson when he nodded in the winner.
Hanley exemplified the spirit of Steve Kean's Blackburn of late. A draw at Anfield last week has now been followed up with arguably the greatest victory of his managerial career.
The win, which bookies had at 28-1 prior to the match, moves Rovers off the bottom, and only three points shy of 17th.
It should give Kean some respite from the supporters, who have been calling for his resignation.
There will not be calls for Ferguson to resign after this loss, but fans and the Scot will be deeply disappointed with United's display, after they missed out on the chance to leapfrog bitter rivals and league leaders Manchester City - and be top of the Premier League going into 2012.
United went a goal behind early on when Berbatov grabbed Samba's shirt as a free-kick was launched into the area - and pulled the Congolese to the ground.
Referee Mike Dean was perfectly positioned to see the foul and pointed to the spot. Yakubu, with little back-lift, calmly slotted past David de Gea.
Rovers would have been expecting to weather a storm from the restart, but there was no storm.
Both sides were without many regular first-team players, but Blackburn, buoyed by their draw at Anfield last week, were the far better organised.
Ferguson's side were largely limited to half chances, although Nani went close with an angled drive which flew a yard wide, while Javier Hernandez's turn-and-shot also missed the target by a foot.
United were rocked again after the break when Yakubu scored his second to the astonishment of those watching.
The ball bounced off the legs of Michael Carrick but then Yakubu drifted past a static Phil Jones and angled a brilliant strike past De Gea.
But 60 seconds from the restart, United pulled a goal back when Berbatov headed in after Rafael's attempted shot drifted into his path.
And the Bulgarian equalised soon after with his sixth in three games - a shot swept in from 10 yards, following brilliant work from Antonio Valencia down the right.
It was all set for a final flourish from United - but Blackburn continued to press forward, winning a corner on the left.
Morten Gamst Pedersen swung the ball into the area and the impressive youngster Hanley, 20, beat De Gea to the punch with his first header before nodding in the follow-up.