PARIS - Critics have often questioned Alexander Zverev's mental toughness but when it comes to five-set marathons at the French Open the German's fortitude cannot be doubted.
On Wednesday the 23-year-old sixth seed was nowhere near his best against French doubles specialist Pierre-Hugues Herbert but chiseled out a 2-6 6-4 7-6(5) 4-6 6-4 victory.
He has now won all six of his matches that have gone to a deciding fifth set in Paris and six of his last seven anywhere -- the one loss coming in a heartbreaking defeat to Dominic Thiem in this month's U.S. Open final.
"I'm pretty fit," Zverev said after battling Herbert for a minute under four hours when asked for the key to his success in fifth-set deciders. "You know, sometimes I just feel like I find a way, like today. Today I was not the better player on court.
"I was not doing anything better than he did. But I found a way, which was the most important. But, yeah, I think I lost the most important five-setter in my career so far, which is upsetting but it's okay."
Zverev was two sets ahead in that Flushing Meadows final and also served for his maiden Grand Slam title in the fifth set only to see glory slip through his fingers.
Yet any suggestion he would arrive in Paris a damaged man was put to bed on Wednesday as he showed the kind of fighting qualities for which new coach David Ferrer was renowned.
A flat-looking Zverev wasted two break points in the opening game, then served two double-faults to drop serve.
The skilful Herbert, who has a career Grand Slam in doubles, broke again to take the opener and looked in total control in the second in which he had a point to take a 5-1 lead.
Zverev finally found his aggressive game and hit back to snatch the set before the third set went with serve to set up a tiebreaker. Herbert looked favourite to take it when he had the court gaping at 5-3 but swung a forehand drive volley wide when set points beckoned.
The 78th-ranked Frenchman then lost the next three points.
With a small but vocal crowd urging him on Herbert seized on another Zverev dip in the fourth set to take it into a decider.
Even when Zverev moved 3-0 ahead there was another twist as Herbert produced some dazzling tennis to break back with a searing backhand pass after a dropshot.
Zverev responded to move 5-3 ahead only to falter when serving for the match. But Herbert served a nervy double-fault in the next game and Zverev grabbed his chance.
Zverev will next face Italian Marco Cecchinato who he beat en route to this year's Australian Open semi-final.
(Reporting by Martyn Herman Editing by Toby Davis)