Novak Djokovic faces the first true test of his bid to hold all four Grand Slam titles simultaneously for the second time in the French Open quarter-finals against Alexander Zverev on Wednesday.
The winner of that match will face either last year's runner-up Dominic Thiem or big-hitting Russian Karen Khachanov, who knocked out Juan Martin del Potro in the fourth round.
Here, AFP Sport takes a look at the final two men's last-eight matches on Wednesday:
Novak Djokovic (SRB x1) v Alexander Zverev (GER x5)
Head-to-head level at 2-2
- Djokovic has made serene progress through the first four rounds, losing just seven games on average in each match en route to a record-breaking 10th straight French Open quarter-final.
In stark contrast, Zverev has dropped four sets already and had to come through a five-set battle against Australian John Millman in the opening round, although his form against Djokovic will give him cause for optimism.
The 22-year-old German won their only clash on clay in the 2017 Italian Open final, and also beat the Serbian star in last year's ATP Finals championship match, winning comfortably both times 6-4, 6-3.
But Zverev had endured a mediocre clay court season until the eve of Roland Garros when he clinched the Geneva title, playing on a last-minute wild card.
The 6ft 6in (1.98m) Zverev admitted that his patchy form in 2019 has also been impacted by off-court issues.
He is involved in a legal battle with his former manager which has left him increasingly distracted.
"I had to do a lot of things that I usually don't do, a lot of management stuff, a lot of lawyer stuff, so things that I'm not used to doing," he said.
Djokovic could become only the second man, after Rod Laver, to hold all four Grand Slams at the same time twice with a second French Open title this week, and is hoping the longer format could play into his hands against Zverev.
"Sascha (Zverev) probably was not satisfied with his results in the big events before," said the world number one. "Grand Slam is best of five. It's different."
Dominic Thiem (AUT x4) v Karen Khachanov (RUS x10)
Khachanov leads head-to-head 1-0
- Thiem, who lost last year's final to Rafael Nadal, is looking to reach a fourth straight French Open semi-final.
But he faces an opponent who unleashed a barrage of massive serves and forehands to overpower former US Open champion Del Potro in the last 16, and also won their only previous meeting in the 2018 Paris Masters semi-finals en route to the biggest title of his career to date.
His run in Paris, the third consecutive year he has made the second week, means Khachanov will break into the world's top 10 for the first time after the tournament.
"I will try to fight and let's see. Let's see what happens," said the 23-year-old Russian, whose pregnant wife was cheering him on during a dramatic win over Del Potro.
The 25-year-old Thiem is still waiting for a maiden Grand Slam title, but was happy to reserve some energy in a straightforward win over dangerous Frenchman Gael Monfils last time out.
"Of course it's very important, because, I mean, we all hope that we're here for two weeks," he said. "And two weeks in a Grand Slam, it can be very long."