Together the Swiss duo teamed up to win an Olympic doubles gold medal at Beijing in 2008 and the country's first and only Davis Cup triumph six years later.
On Thursday, however, their friendship will take a back seat when they walk out on Rod Laver Arena for an Australian Open semi-final that promises to be one of the highlights of the season-opening grand slam.
It will be the 22nd time the pair have met and Federer, back after six months out and shortening as the bookmaker's favourite to capture his fifth Australian Open crown, has won 18 of the head-to-head match-ups.
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He has also looked to be back to his best in beating 10th seed Tomas Berdych, fifth seed Kei Nishikori and then destroying Mischa Zverev, who had upended world number one Andy Murray, in the quarter-finals.
While Wawrinka was won just three of their clashes, the 35-year-old Federer places no such stock in that statistic. All that matters is how his opponent pitches up in their next match.
And with someone like Wawrinka, the 17-times grand slam winner knows how much his 31-year-old compatriot has progressed since their first meeting indoors in Rotterdam in 2005.
Back then Wawrinka, he said, struggled with the faster surfaces. His footwork was not there. You could tell from the other side of the net that he did not enjoy playing on grass or hard courts.
So the younger Swiss did what anyone would do. He sought advice and Federer became a counsellor of sorts.
Gradually, as the calls became less frequent, Federer realised that Wawrinka had 'got it'.
CLAY DNA
"What I like with Stan is if I would tell him something, I felt like he was able to do it," Federer said. "That showed me that he's a great player, that he's got a mind of somebody who understands what I'm trying to explain to him."
Federer said the mentoring had stopped well before Wawrinka won his maiden grand slam at the Australian Open in 2014, though the fact he did it at Melbourne Park was a surprise given his early struggles on hard courts.
"If I would have called any grand slam for him to win it was always going to be the French, because he moved so effortless on clay. That's his base. That's his DNA really," Federer added.
"I think he's done incredibly well on all the other surfaces, including grass actually, also indoors, hard and fast.
"He's become such a good player, I super respect that, that the guy is able to transform his game around like that, in his footwork, in his mind, also in his game plan.
"That's his transformation, and I like what I saw."
Wawrinka's transformation now includes two more grand slam titles, including last year's U.S. Open, and while he typically has a downbeat approach to his matches, the world number four is confident he has the game to beat Federer.
"I'm more confident with myself. When I step on the court, doesn't matter who I play, I know what I have to do if I want to win," said Wawrinka, who was taken to five sets by Martin Klizan in the first round but has improved with each ensuing match.
"Against Roger, it's always special because he's so good. He's the best player of all time. He has answers for everything.
"But I managed to beat him in a grand slam, so we'll see."
(Writing by Greg Stutchbury in Wellington; Editing by John O'Brien)
