The veteran Portuguese defender, who was making his return from injury, admitted that his Spanish rival's headed goal effectively decided the game in the visitors' favour
Los Blancos had reached the interval a goal to the good thanks to Cristiano Ronaldo’s early strike, but Puyol drew the visitors level with a header from a Xavi corner just four minutes into the second half.
Barca never looked back and claimed a deserved victory with a 77th minute goal from another defender, Eric Abidal.
Xavi claimed afterwards that Barca's equaliser had been a goal of the utmost psychological importance and Carvalho did not disagree with that assessment.
“We were fine and playing a tight and balanced game, but Puyol's goal after half-time changed everything,” the veteran defender told his club's official website.
“Barcelona became more confident and their game improved. We'll do everything we can to turn the tie around."
The quarter-final first-leg tie represented Carvalho’s first appearance for Madrid in months after his recent struggles with back and knee problems and the Portuguese centre-half admitted that he was relieved to have finally returned to competitive action.
"It's been a complicated year for me because I played many games last season and I've experienced physical problems from the start of the present campaign,” he explained.
“But I feel better each day and expect to return to last season's form.”
Madrid face Athletic Bilbao away in La Liga this weekend before travelling to Barcelona next Wednesday for the second leg of their quarter-final tie.
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