Bottom club Blackburn Rovers wrecked Sir Alex Ferguson\'s 70th birthday celebrations on Saturday after scoring a stunning 3-2 victory over Manchester United at Old Trafford. Rovers defender Grant Hanley bundled in an 80th-minute winner after United goalkeeper David de Gea made a hash of his punched clearance from Morten Gamst Pedersen\'s corner. Hanley\'s decisive goal settled a bizarre encounter that had seen Rovers surge into a 2-0 lead via an Ayegbeni Yakubu brace before Dimitar Berbatov struck twice to level it for United. The defeat ruined United\'s hopes of finishing 2011 on top of the Premier League and handed rivals Manchester City the opportunity of opening up a three-point lead with a win at Sunderland on Sunday. The win was only Blackburn\'s third of the season and their first victory away from home. Rovers grabbed a shock lead on 16 minutes when Yakubu stroked home from the penalty spot after Berbatov had hauled down Christopher Samba to concede a foul. United dominated the remainder of the half but struggled to find a way through some resolute Rovers defending. A central midfield comprising Rafael Da Silva and Park Ji-Sung failed to ask serious questions of the Blackburn defence, while United badly missed the attacking thrust of the rested Wayne Rooney. And on 51 minutes United were left reeling when Yakubu bulldozed through some feeble United defending to drive in his second for 2-0. United responded almost immediately, however, sweeping forward from the re-start and pulling a goal back through Berbatov when the Bulgarian headed in Rafael\'s angled shot. On 62 minutes Berbatov levelled a pulsating encounter, sweeping in from close range after a fine run and cross from Antonio Valencia. It seemed as if United were poised to go and claim the victory but de Gea\'s blunder gifted a precious victory to Steve Kean\'s Rovers.