MONTE CARLO, Monaco - Third seed Alexander Zverev came through a three-set tussle with fellow German Jan-Lennard Struff on Thursday to set up a possible Monte Carlo Masters quarter-final with his brother Mischa.
The 20-year-old, who won two Masters titles last season, became frustrated in the second set but came through 6-4, 4-6, 6-4 and will play either his older brother Mischa or Richard Gasquet in the last eight.
"Hopefully my brother will win and it will be an amazing day on Friday," said the younger Zverev.
The world number four claimed the opening set thanks to a break in game seven, before a bizarre second set in which both players struggled on serve.
Zverev became increasingly frustrated as he constantly gave away leads, complaining that advertising cushions on the side of the court were dangerous.
Struff claimed the set to level the match with the seventh break of serve in only eight games, as Zverev hurled his racquet to the ground in anger.
He refound his range in the decider, though, racing into a 5-2 lead with a double break.
Zverev was broken to love when serving for a place in the last eight and then missed a match point in Struff's following service game, but finally got over the line as his opponent fired wide.
Belgian sixth seed David Goffin held off a late fightback from Roberto Bautista Agut to reach the last eight with a 6-4, 7-5 win, in a match that saw the Spaniard accidentally hit a ballboy with the ball.
The 11th seed was broken to slip 4-1 down in the second set, and when returning the ball to the other side of the net, saw it strike a ballboy as he ran across the front of the net.
"I just saw the ball going straight to the ball boy. I was surprised he only had a warning. For me, if you send a ball at the head of a ball boy, you're out," said Goffin.
"I don't know what the rules are exactly and how he could get a warning. He was saying the ball bounced, and the ball boy was there by coincidence. Unlucky for him."
Meanwhile, Canadian Milos Raonic pulled out of the tournament before his third-round match against Marin Cilic on Thursday with a right knee injury.
The 14th seed, a former Wimbledon runner-up, struggled with the problem during his second-round win over Marco Cecchinato on Wednesday.
Second seed Cilic progresses to a last-eight tie with either Italian qualifier Andreas Seppi or Japan's Kei Nishikori.