Zverev says he spends up to four hours each day working on weights and fitness.
The Austrian seventh seed, the last man to beat claycourt master Rafa Nadal on his favorite surface, displayed an impressive arsenal of weapons in the first two sets before regaining his composure after the loss of the third.
These hurdles have finally been overcome, but Zverev has had to dig deep. If you do, leave this match alone from a pre-match betting point of view, but if you feel that Zverev will be as fresh as a daisy, then Zverev at [2.56] would be a viable consideration.
Dominic Thiem celebrates winning his fourth round match against Japan's Kei Nishikori.
The Austrian blew the Monte Carlo finalist away within the first two units, misplaced the third, however got here by means of 6-2 6-Zero 5-7 6-Four to land in a 3rd consecutive Roland Garros quarterfinal. In all three of his five-setters he has trailed 2-1 in sets. "I'm very happy about being in the quarterfinals here going the hard way, going the long distance. showing everybody that I can play for as long as I need to".
"I don't know if I'm going to play on grass", Djokovic, who won the last of his 12 Grand Slam titles in Paris two years ago, told reporters crowded into a small interview room after he declined the opportunity to use a much larger one.
Despite saving the point with a ruthless serve after his disagreement with the umpire, Zverev surrendered the first set lead to Khachnov with a netted backhand.More news: Bill Clinton: I Do Not Owe Monica Lewinsky an Apology
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Djokovic eased past Spanish veteran Verdasco 6-3, 6-4, 6-2 and will play in the last eight at Roland Garros for a record 12th time. "So I don't know where he was completing and what he was completing, because I think if we watch on the Hawk-Eye, the ball is totally out". Incredibly, this was nearly replicated by Fabio Fognini, who looked down and out after two sets, only to take his match with Marin Cilic to a decider, which eventually was taken by the Croat.
The bubbly 21-year-old made the biggest final of her career in Indian Wells in March, beating Wozniacki en route. The Serbian will meet Italian underdog Marco Cecchinato as the latter shocked eighth-seeded David Goffin 7-5, 4-6, 6-0, 6-3.
Keys faces Kazakhstan's world No 98 Yulia Putintseva, who produced the upset of the day to eliminate 26th seed Barbora Strycova of the Czech Republic.
U.S. Open champion Sloane Stephens was in complete control as she broke Estonian Anett Kontaveit's serve five times on her way to a 6-2 6-0 win in just 52 minutes.
He was fortunate to survive a break point when serving for the set at 5-3, before drawing level at two sets apiece with an ace.
To say that Zverev has endured a hard route to the last eight would be some understatement.
Asked whether he could have envisioned, even as recently as April, that he would get this far at a major tournament, Cecchinato answered with one word, "No", before breaking into as wide a smile as can be.