Novak Djokovic improved to 19-0 in the first round of the U.S. Open, battling through some leg troubles to beat Learner Tien 6-1, 7-6 (3), 6-2 on Sunday night.

Djokovic had his hands on his knees multiple times in the second set and received treatment on his right big toe after it. But after having his serve broken in the first game of the third set, he won the next five games to regain control.

It was the 24-time Grand Slam champion's first match since Wimbledon and one that made it tough to tell if the 38-year-old remains a real contender to win a fifth title in Flushing Meadows. He rolled through the first set in just 24 minutes, then looked weary in a second set that took nearly an hour longer.

The No. 7-seeded Djokovic has made a career of wearing down his opponents, but he looked

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