Paris - Four years after his defeat to Stan Wawrinka in the Roland Garros quarter-finals prompted him to call a temporary halt to his Paris aspirations, Roger Federer renews his rivalry with his oldest friend with a place in the semi-finals at stake on Tuesday.
Federer, the 37-year-old 2009 champion in Paris, holds a 22-3 stranglehold over Wawrinka, 34.
But all three losses have come on clay, including in the last-eight at the 2015 French Open as Wawrinka went on to claim a second a second career Slam title.
"I have a bad memory of it. Stan beat me in three sets with his terrible shorts," said Federer in reference to his compatriot's gaudy, checked shorts, compared by some to a tablecloth pattern.
Federer, a 20-time major winner, is the oldest man to make the quarter-finals of a Slam since Jimmy Connors at the 1991 US Open.
He has glided into his 12th Paris quarter-final and 54th at the majors, spending just over seven hours on court.
Wawrinka, on the other hand, has needed 12.5 hours to get to his first Slam quarter-final since the 2017 French Open when he lost to Rafael Nadal in the final.
Just over five of his hours on court at Roland Garros were spent disposing of sixth seed Stefanos Tsitsipas in the last-16 in the fourth longest match ever played at the tournament.
Wawrinka's run to the quarter-finals would have looked unlikely this time last year when the legacy of two knee surgeries in 2017 saw him lose in the first round in Paris.
That saw him drop out of the top 250 in the world.
"I'm just happy for the guy that he's back after his knee problems," said Federer of his 2014 Davis Cup and 2008 Olympic gold medal winning team-mate.
"They were severe, and that's why I think he's really happy he got sort of a second life on tour.
"It's nice to see him pain-free and playing well. I hope he's not at the level of '15, but we'll find out, because there he was crushing the ball. It was unbelievable."
Wawrinka, now back at 28 in the world, says it will be amazing to face Federer again despite having lost their last six meetings since his 2015 landmark moment.
"He didn't play here for so many years. He's still playing so well. He's the best player to ever play this sport. So it's going to be a big challenge," said Wawrinka, the holder of three Grand Slam titles.
"I didn't beat him many times in my career, but I did once here, so I still do remember that time and was a special day for me.
"I'm getting old and older and older.. and he's better than me, also, so never forgot that."