After the first set, a doctor had to attend to Djokovic's right shoulder and neck. In the following set, the Serbian player required further treatment for his right arm. Previously, during his third-round victory against Cameron Norrie, Djokovic needed medical attention for back pain.

Djokovic serves during his match against Struff in the fourth round of the US Open at Arthur Ashe Stadium, New York on 1/9. Photo: *Reuters*

Despite the physical issues, Djokovic performed impressively against Struff. Even with recent wins against Holger Rune and Frances Tiafoe, Struff struggled to find his rhythm against Djokovic.

Struff's serve is considered his strongest weapon, but the German player committed six double faults. He had fewer than half as many aces as Djokovic (6 compared to 12). This inability to capitalize on his serve led to Struff being broken six times.

In contrast, Djokovic maintained a consistent serving performance with a first-serve percentage of 79%, alongside 33 winners and only 20 unforced errors. The 38-year-old outperformed Struff in all these statistics.

"I saw the stats, and I served much better than my opponent, who is one of the biggest servers on the tour," Djokovic said in his on-court interview. "That was great; it allowed me to have an easier time on the court. It made points shorter. I was very pleased with my serve from the last match and today."

Djokovic advanced to his 14th US Open quarterfinal, where he will face Taylor Fritz. Djokovic holds a perfect 10-0 head-to-head record against Fritz, having dropped only three sets in their 26 sets played.

Vy Anh