Stanislas Wawrinka has admitted that he "wasn't there mentally" during the second set of his match against Donald Young at the US Open.
The French Open champion dropped a set for the first time at Flushing Meadows this year on his way to a four-set victory over the American.
The fifth seed told reporters: "The set was so quick. I wasn't there mentally. Calmed down a little bit. I began to be more aggressive, started moving my feet better.
"He had the crowd. It was a tough match for sure. It was a great atmosphere. Sometimes you don't control yourself. You need to put the pressure out. I played really well after."
Wawrinka will face the winner of the match between former champion Andy Murray and South Africa's Kevin Anderson.
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