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 is on a race against time to clinch his 25th Grand Slam title. Since winning his 100th career title at the Geneva Open, the Serbian has only shown up for the Grand Slams.

Novak Djokovic looked tired. He looked hurt. And at times Sunday night, he just looked old. Djokovic overcame all that and improved to 19-0 in the first round of the US Open, battling through some leg troubles to beat Learner Tien 6-1,