HALLE, Germany -- World No. 1 Jannik Sinner reached the Halle Open semifinals by battling to a 6-2 6-7(1) 7-6(3) win over German Jan-Lennard Struff on Friday.
Struff, who is 34 and had just upset sixth-seed Stefanos Tsitsipas in the last 16, challenged the Italian, hitting 18 aces and saving 16 of 18 break points in the 2½-hour contest.
"It was a very tough match," Sinner said after his third consecutive three-set win. "I had chances in the second set and chances in the third, but I couldn't take them.
"I just tried to accept these kind of challenges. It was very tough mentally.
"I played a lot yesterday and today. Two hours on grass is a long time. I'll try to recover for tomorrow. Hopefully I'll show some good tennis."
Sinner, playing his first tournament atop the ATP world rankings, will face the winner of the clash between China's Zhang Zhizhen and Christopher Eubanks of the United States.
German Alexander Zverev also reached the semis, rallying after dropping a first-set tiebreak to Frenchman Arthur Fils to prevail 6-7(5) 6-3 6-4.
The world No. 4 will face Polish fifth-seed Hubert Hurkacz, who defeated American Marcos Giron 7-6(5) 6-4.