The Portuguese criticised his team's tactics after their 2-0 semi-final first-leg defeat, his only consolation being that Real will be forced to attack in next Tuesday's return if they want to have any chance of making the final.
Ronaldo, whose 42nd goal in all competitions this year gave Real a 1-0 victory over Barca in the King's Cup Final last week, could only fume in frustration at his team's defensive approach.
"I don't like it, but I have to adapt because that's the way it is," the world's most expensive player told reporters.
While Ronaldo struggled, World Player of the Year Messi rose to the occasion, scoring twice after Real midfielder Pepe had been sent off.
The 23-year-old Argentine took his season's tally to 52 in all competitions, including an unrivalled 11 in the Champions League, with a clever near-post flick and a mesmerising second that left Real defenders trailing in his wake.
Messi and Ronaldo are the only players to have scored so far in the four-match series of 'Clasicos' being played over 18 days.
A penalty apiece in the 1-1 La Liga draw 10 days ago was followed by Ronaldo's towering header for the extra-time winner in the cup final, but Messi proved the difference on Wednesday as a more aggressive Barca took control of the game.
URGED FORWARD
They had 71 percent of possession while Real sat back rather than press higher up the pitch as they had in the cup final and Ronaldo could be seen angrily gesticulating at his team mates as he urged them forward.
"It's much easier against 10. I wish I could get the chance to play against 10 like he did," Ronaldo said referring to Messi's performance.
"At 2-0 down and away from home... anything can happen in football, but we know it will be very difficult," he said of the side's chances of making the final in London on May 28.
Barca's players were cautious about the second leg and brushed off Real's complaints over the refereeing.
"This time justice has been done and I think football has won," Spain midfielder Xavi told reporters.
"Their play is speculative and they have no other recourse except to play dirty, as their coach (Jose Mourinho) has instilled in them. We have never sacrificed our style."
Barca defender Gerard Pique added: "The sending-off wasn't the key, because for the first 60 minutes Real didn't try to play football either.
"When you play to the limits of violence, sometimes you get burned."
