Nani's controversial red card became the turning point of the battle at Old Trafford Tuesday as Real Madrid knocked out Manchester United 3-2 on aggregate to reach the last eight of Champions League.

United, who paved the way for a promising quarterfinal berth after a first leg 1-1 draw at Madrid, seemed on course three minutes after the restart.

Danny Welbeck and Robin van Persie's shots were both denied by Real's blocks. However, defender Sergio Ramos failed to clear Nani's subsequent low cross and kicked it past his keeper Diego Lopez to score an own goal.

United, with the lead, suffered a huge blow just seven minutes later.

Nani, a ceaseless threat to visitors on the left flank, was shown a straight red card after he made a aerial challenge on Real's right back Alvaro Arbeloa.

"Independent of the decision, the best team lost," said Real manager Jose Mourinho after the tie.

"I doubt that 11 against 11 we win the match," he added.

Real showed their bench depth in the 66th minute. The ex-Tottenham playmaker Luka Modric came off the bench, rounded one United player at the edge of the box and then delivered a 20-yard powerful shot to beat keeper David de Gea.

Just three minutes later, Cristiano Ronaldo, who returned to Old Trafford for the first time since his 2009's move to Real, stunned the home team as the Portugese winger picked up a sharp low cross from Gonzalo Higuain at far post to seal the 2-1 victory.

In front of the fanatic 74,959 crowd, Ronaldo lowered his head, waved arms and made few celebrations.

"It was unbelievable. It was an emotional moment for me tonight," said Ronaldo, referring to the warm welcome he got from United fans before the kick-off.

United manager Sir Alex Ferguson protested against the red card decision during the match. He didn't attend the post-match press conference.

"It's a distraught dressing room and a distraught manager. That's why I am sitting here," said assistant manager Mike Phelan.

He said the decision was disappointing and spoiled the game.