Alexander Zverev had not played a five-set match in two previous visits to Roland Garros. On Sunday he completed his third in five days, guided by his Russian-born father, to beat the talented young Muscovite Karen Khachanov 4-6, 7-6 (4), 2-6, 6-3, 6-3 in just under three and a half hours.

To borrow from Fred Trueman, if the 21-year-old Zverev does win this French Open “he’ll be bloody tired”, although he gave no indication he was about to collapse in a heap on Court Suzanne Lenglen after breaking down the resistance of the 22‑year‑old Khachanov, the world No 38.

The two youngest players left in the draw needed all the energy of youth on a hot, still day. Zverev, seeded second here in Roger Federer’s absence, will take 11 hours and 46 minutes of muscle-sapping baggage into the quarter-finals against the bustling Austrian Dominic Thiem, who stopped him in the third round two years ago.

That might not be long by the standards of the past decade but, cumulatively, it is a significant workload, and one Zverev says he is still getting used to, although he bridles at suggestions he lacks staying power over five sets – and he now has a respectable 6-6 record.

Asked if he thought Khachanov was flagging at the end, he said: “At the beginning of the fourth I thought ‘OK I can turn this match around’, especially when I saved a few break points. He’s a very fit player, so I don’t think it’s that easy to make him tired. Obviously playing five sets, anyone would get tired a little bit.”

He added: “I know who I am. It’s not about learning any more. 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. I’m very happy about being in the quarter-finals here, going the hard way, going the distance every single time and showing myself, showing everybody, that I can play for as long as I need to. 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.”

Thiem, who outlasted a weary Kei Nishikori 6-2, 6-0, 5-7, 6-4, is one of the busiest and quickest players on clay. There will be no rest for Zverev when they return on Tuesday.

“That’s the match-up most of the fans in Germany and Austria were hoping for when they saw the draw,” Thiem said. “We just played in Madrid [where Zverev won in the final]. He’s an amazing player – probably now the third-best after Rafa [Nadal] and Roger.”

He did not expect stamina to be a problem for Zverev. “He has an amazing team [including Andy Murray’s former conditioner, Jez Green]. He’s super fit.”

For Zverev to become the first from his country to win the title since Henner Henkel beat Bunny Austin in 1937, he has to win three more matches. The most daunting challenge will be in the final, barring calamity, against the greatest player in history on clay, the 10-times champion Nadal.

To eliminate the Spaniard from the equation, Zverev’s countryman Maximilian Marterer will have to pull off the upset of the tournament, year, decade and millennium on Monday – and then all bets are off. The 22-year-old left-hander from Nuremberg, ranked 70 in the world, can only hope Nadal stubs his toe on the morning of the match.

In the top half of that side of the draw, Novak Djokovic served his way through some scrappy moments to a 6-3, 6-4, 6-2 win against the Spaniard Fernando Verdasco, whose blistered feet in the second set can hardly have added to the experience over two hours and 25 minutes on Chatrier.

Having dropped just one set on his way into the second week, he said courtside: “I like my connection with the public here. He’s a clay specialist and it wasn’t an easy match. He stayed concentrated with a good deal of intensity.”

Djokovic has an unexpected opponent in the quarter-finals – the 25‑year‑old Sicilian world No 72, Marco Cecchinato, who upset David Goffin 7-5, 4-6, 6-0, 6-3, and becomes the lowest-ranked man to get this far here since Ernests Gulbis in 2008.