By Martyn Herman
PARIS (Reuters) - Alexander Zverev is destined to win a Grand Slam title but how long that breakthrough takes depends on when he develops a more ruthless streak, according to one of the sport's toughest competitors Mats Wilander.
The 22-year-old German fifth seed made heavy weather of beating Australian John Millman in the first round, letting slip a two-set lead before scraping home in five sets.
He had a succession of five-setters 12 months ago in Paris before bowing out to Dominic Thiem in the quarter-finals, still surprisingly his best showing in a Grand Slam tournament.
Speaking to Reuters, Eurosport analyst Wilander, twice a champion at Roland Garros, said Zverev should learn from two of the game's greatest front runners, Rafael Nadal and Roger Federer and save himself extra leg work.
"Two sets to love doesn't do it in Grand Slams," Wilander said. "That's something he needs to get used to doing. It's like an equation. How hard do you press when you are two sets up? Or wait for the other guy to fold. I think most probably he hasn't quite figured it out.
"When you are two sets up you have to reinvent the tactics a little. When Nadal wins the first two sets and Federer they are going further forwards and they go harder, risking more.
"I think Zverev tends to invite opponents back."
Zverev faces 20-year-old Swede Mikael Ymer next, an opponent ranked 148th in the world but who Wilander believes will go in undaunted because of Zverev's patchy Grand Slam record.
"Ymer goes in knowing he has a chance to win even if Zverev is solid in the top five or six in the world, mainly because of because of Zverev's Grand Slam record," Wilander said.
"It's good that Zverev won a close match on Tuesday, but it was another two hours of physical work and mental energy.
"It reminds me a bit of Caroline Wozniacki. It took her a while, too long, to figure it out and she may now only win one Slam. I think with Zverev, he will win a Slam.
"But he has to stop worrying as much about losing, go out of the comfort zone, risk it a little bit more. Sometimes the way he plays, it's like he think 'I know I'm going to win and I will just hang out until match point.
"That can catch up on you."
(Reporting by Martyn Herman; Editing by Christian Radnedge)