Marin Cilic: I've reached quarter-finals without using up energy

The 28-year-old Croat joins four other grand slam winners in the last eight but, while nine-times Roland Garros winner Rafa Nadal, holder Novak Djokovic, 2015 champion Stan Wawrinka and Andy Murray make the headlines, Cilic barely gets a mention.

On Monday he was on court for 48 minutes before South African Kevin Anderson retired because of a leg injury with Cilic leading 6-3 3-0 on Court Suzanne Lenglen.

The undemonstrative seventh seed joined Spain's Nadal and Austrian Dominic Thiem in reaching the quarters without conceding a set and will next face Swiss Wawrinka, who he trails 11-2 in head-to-heads and has not beaten since 2010.

Only Nadal (20) has lost fewer games so far here this year and Cilic, who has reached the quarter-finals for the first time having done so in the other three slams, says he has not felt better at a grand slam since he won the 2014 U.S. Open.

"Apart from at the US Open in '14, I'm definitely feeling the best on the court," Cilic, the first Croatian to reach the last eight since Mario Ancic and Ivan Ljubicic in 2006, told reporters. "Even then I didn't go through the draw as comfortably as here."

At 1.98 metres, and with a game built on power off the serve and forehand, Cilic does not look made for clay.

But he is a French Open junior champion and has two claycourt titles to his name, one of which came this year when he won the Istanbul tournament.

"With the form I'm in I feel great on the court," said the 28-year-old. "It's a huge bonus for me, knowing that mentally and physically I haven't spent any energy at all.

"I grew up on clay, playing half the year on clay. But I would say last year I started to feel that I'm getting better on it. This year we changed a little bit the routine of the training on clay, and that helped me a lot."

Cilic will need to find another gear against third seed Wawrinka, but he is ready and with warm weather expected later in the week he definitely has a puncher's chance.

"With Stan it's extremely difficult on any surface," he said. "He has won a lot of matches in a row against me.

"But for me I have to focus on keeping this level and to look for my chances."

For Anderson a decent run ended in frustration and he just hopes he will recover in time for the grasscourt swing.

"The serve was not firing properly. I wasn't able to use my legs properly. As the match went on, movement became increasingly difficult," he sai