MONACO -- Third-seeded Alexander Zverev has reached the Monte Carlo Masters quarterfinals, where he could meet his brother.
Mischa Zverev was to play Richard Gasquet later Thursday.
"Hopefully my brother will win and it will be an amazing day tomorrow," the younger Alexander Zverev said.
He made hard work of closing out German countryman Jan-Lennard Struff 6-4, 4-6, 6-4.
Zverev was broken to love serving for the match at 5-2 and wasted a first match point when Struff served at 30-40 in the next game.
Struff could have made it even harder for Zverev, but he missed an easy volley at the net at 30-30. Instead of giving him break point, it gave Zverev a second match point. He took it when Struff hit a powerful forehand narrowly wide, and let out a yell of relief.
Defending champion Rafael Nadal was to play Karen Khachanov, and two-time winner Novak Djokovic was facing No. 5 Dominic Thiem later Thursday.
Second-seeded Marin Cilic advanced without hitting a ball after Milos Raonic pulled out with a right knee injury. It was not immediately clear how Raonic injured his knee. Cilic, the Australian Open runner-up, will play Kei Nishikori or Andreas Seppi.
Sixth-seeded David Goffin of Belgium made it through after beating Roberto Bautista Agut of Spain 6-4, 7-5.
After dropping his serve to trail 4-1, Bautista Agut cleared a ball from the back of the court just as the ball boy was sprinting across the court. The ball was travelling slowly, bounced and clipped the ball boy on the head. Bautista Agut raised a hand up in apology.
Bautista Agut had apparently not seen him, because he was looking down at the ball when he swiped at it.
Goffin was confused by what happened.
"I just saw the ball directly hitting the ball boy. I was surprised to see he only got a warning," Goffin said. "For me, if you send a ball onto the ball boy's head, you're (kicked) off. I don't know what the rules are exactly, how he only got a warning. He said the ball bounced and the ball boy just happened to be there. Bad luck for him. But in any case, it's just an incident."
Serving for the match at 5-2, Goffin wasted two match points, lost the game, and then the next two for 5-5.
Goffin, a semifinalist here last year, plays either No. 4 Grigor Dimitrov or Philipp Kohlschreiber in the last eight.