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The home side had the majority of the possession in the opening 15 minutes, but created few chances during that time.
Klaas-Jan Huntelaar had a chance to give the German side the lead just before the break, but his effort finished high and wide.
Ronaldo had the opportunity to score his 13th goal of the competition this season early in the second half when he picked up a header forward from Ramos, but Ralf Fahrmann was able to keep the effort out.
The striker remained a threat throughout the second half, and managed to add his second goal of the night, and fourth of the tie, with a powerful strike into the bottom corner.
Carlo Ancelotti's men extended their lead further just a minute later as Morata tapped in after Ronaldo had rattled the crossbar looking for his hat-trick.
Ronaldo continued to push for his hat-trick in the final minutes of the clash, hitting the post with a low effort five minutes from full time, but he could not find a third before the end of the match.