The visitors enjoyed a flurry of early chances, with Benzema responsible for the best two. He first lifted a shot over the keeper and just wide before seeing another effort tipped away by Roberto.
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The Frenchman was not to be denied for long, however, as he opened the scoring at the third time of asking in the 10th minute. Cristiano Ronaldo failed to control a pass into the box but Benzema was on hand to smash the ball in from close range.
Carlo Ancelotti's men continued to have the better of the half but couldn't find a second goal before the break.