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.

Novak Djokovic’s first match at the US Open was a bit of a litmus test for the Serbian legend because he didn’t play a hardcourt warm-up tournament coming into the year’s final Grand Slam. The 24-time Grand Slam champion said he didn’t play the Cincinnati Open because he prefers to focus on the Grand Slams at this stage of his career.

Novak Djokovic, aiming for his 25th Grand Slam title, overcame American teenager Learner Tien in the US Open first round despite a foot blister requiring a medical timeout. The Serbian secured a 6-1,