MANCHESTER, United Kingdom (AFP) - Cristiano Ronaldo admitted he felt "sad" after his goal ended former club Manchester United's involvement in the Champions League and put Real Madrid in the quarter-finals.

The Portuguese forward struck a 69th-minute winner at Old Trafford on Tuesday as Madrid fought from behind to earn a 2-1 win on the night and a 3-2 aggregate victory.

The 28-year-old, who spent six highly successful seasons at United, received a round of applause prior to kick-off and made a point of not celebrating his winning goal.

"The reception was unbelievable. It was an emotional moment for me, for both games, especially tonight," he told Sky Sports. "I do not have words to explain how I feel. The supporters made me feel shy as I did not play how I play all the time. Anyway I helped my team, and I feel a little happy inside. On the other hand I feel sad as Manchester United are out."

The game's turning point arrived in the 56th minute, when Ronaldo's international colleague Nani was contentiously shown a straight red card for a high challenge on Alvaro Arbeloa.

Nani had forced Sergio Ramos to put through his own goal eight minutes earlier, but Madrid immediately capitalised on his dismissal, with Luka Modric equalising in the 66th minute before Ronaldo notched the winner.

"To be honest, I did not see what Nani did, but these situations happen in football," Ronaldo said.