For the last couple of seasons, Alexander Zverev has been pegged by pundits as a player who will win multiple grand slam titles before all is said and done. He has given every indication that he can accomplish this with wins under his belt against the best in the game, including Novak Djokovic, Stan Wawrinka, Dominic Thiem and Roger Federer (twice). He entered Roland Garros with three Masters 1000 championships but critics continued to cite the fact that he had never reached a quarterfinal at a major. That changed on Sunday after the German defeated Karen Khachanov 4-6, 7-6, 2-6, 6-3, 6-3.

There does continue to be some cause for concern as Zverev has faced three consecutive five-setters and has trailed in each one. He, also, required treatment on his injured foot in the fifth set against Khachanov. However, despite his 11 hours and 46 minutes on court thus far at Roland Garros, he has survived and advanced and will now clash with Dominic Thiem, with the winner advancing to the semifinals.

“I know who I am. It’s not about learning anymore. It’s about trying to find a way and trying to win. That’s what I am able to do in the last few matches, and I’m very happy about that, said Zverev. If you’re mentally fatigued, then something is wrong with you. Physically, it’s not easy to play back‑to‑back‑to‑back five-set matches – but I will manage it somehow.”

He will have to manage it against one of the more fitter players on tour in Thiem who, by contrast, has won his last three matches in four sets each.

Given recent play, the survivor of the Zverev-Thiem match would be the top candidate to defeat 10-time Roland Garros champion, Rafael Nadal. Zverev won the Madrid Masters a few weeks ago, defeating Thiem in the process. Meanwhile, it was Thiem who last defeated Nadal on his way to that Madrid final. The Austrian has also defeated Nadal three times in the last two seasons, all on clay. But Thiem has yet to beat the Spaniard in a five-set format and won just 7 games against Nadal in the semifinals of last season’s edition of the French Open. Zverev has never defeated Nadal but pushed him to five sets at the Australian Open in 2017.

Nonetheless, Zverev is certainly exuding confidence in the current state of his game. “I'm very happy about being in the quarter-finals here,” he said. “Going the hard way, going the long distance every single time and showing myself, showing everybody, that I can play for as long as I need to.”

Perhaps, breaking down the barrier of having never advanced to a grand slam quarterfinal is part of Zverev’s ascent to the top of the game where he will eventually fill a trophy case full of major titles. And, perhaps he is the heir apparent to the throne of best in the world. He still has plenty of work to do, but the 21-year-old appears keen to face that head-on.