Tennis - Rejuvenated Cilic hails 'mental toughness' after ban

Despite the Croatian's initial claims that a knee injury was hampering his progress, it was later revealed that Cilic had tested positive for banned stimulant nikethamide in April 2013 and the International Tennis Federation handed him a nine-month ban in September.

The ban was reduced to four months after he appealed on the grounds that he had inadvertently taken the substance in glucose tablets and Cilic is now drawing on the experience of that unfortunate chapter in his career.

"For me, the most important part was that I found some mental toughness out of all of that," Cilic said of the ban after beating Chardy 7-6(8) 6-4 6-4 in the fourth round.

"When I came back it sort of gave me more motivation to work and use every opportunity I had to be prepared for every tournament. I used that time as well for physical preparation, I was doing a lot ... Overall, I am feeling very well and I think my game is at a high level."

Cilic, who became the fourth Croatian man to reach the Wimbledon quarter-finals, fired 33 aces past Frenchman Chardy and is delighted with his serve's increasing dependability.

"The serve has become a big weapon and I can rely on it during the matches," he told reporters. "I felt in some points that Jeremy was guessing where the serve was going to go and he was making some mistakes."

Cilic, the 26th seed, is coached by compatriot Goran Ivanisevic and says that he is also benefiting from the guidance of the charismatic former Wimbledon champion.

"All the things we are working on, they're working for me on the court," Cilic said.

"Having him over here beside me is definitely another big plus. He's been in the second week of Wimbledon many times, so of course I'm leaving all the small details up to him."