-- PARIS -- Even a 17-time Grand Slam champion, it turns out, succumbs to daydreams.
"Everything crosses your mind as you sit at breakfast and you have, for once, a quiet moment when the kids are not there," Federer said after advancing to the quarterfinals here with a win over Gael Monfils. "I'm realistic. I know there is a chance. At the same time, I know how hard it is."
With a favorable draw and his game in good shape, Federer actually let himself contemplate what a second French Open title would mean.
"It would be unbelievable, no doubt," he said. "Clearly, those thoughts also creep into my mind sometimes and go, 'How would that feel again?' Then again, you're like, 'Whew, let's not go that far down the tournament yet.'
"At the same time, sometimes I think, 'How does it feel if I take the plane tomorrow and go home if I lose today?'"
Presumably, the No. 2-seeded Federer will discover the answer to that no longer hypothetical question Wednesday when he flies back to Bottmingen, Switzerland -- the same day Novak Djokovic and Rafael Nadal play their anticipated quarterfinal here.
Federer had beaten Swiss Davis Cup teammate Stan Wawrinka 16 times in 18 tries (and 14 of the past 15), but it didn't happen Tuesday.
Not even close.
No. 8-seeded Wawrinka overpowered Federer 6-4, 6-3, 7-6 (4) to advance to Friday's semifinal match against the winner of the match between Jo-Wilfried Tsonga and Kei Nishikori. There were times when it looked almost too easy for the 30-year-old Wawrinka -- and moments when the 33-year-old Federer, trying to be aggressive by crowding the net, looked a step slow.
"I don't think this is the first for anybody who has seen Stan play this way," Federer said afterward. "We know he can do this.
"It's just nice for him now, even talking for him, to string it together on a big occasion like this at the French where I always thought he'd have his best chance to do well."
It was Wawrinka's first win against Federer in a Grand Slam after going 0-for-4, including two losses at Roland Garros.
"I'm really happy, for sure," an emotional Wawrinka said later. "Really happy. I'm always really, really nervous when I play Roger, especially in the big match. But I play my best when I am that way.
"I'm a little bit surprised to win that match in three sets."
Since winning Wimbledon in 2012 for his record 17th major singles title, Federer has gone 0-for-11. In seven of those instances, he exited before the semifinals. Back in January, Federer lost in the third round of the Australian Open to Andreas Seppi.
This one was reminiscent of the 2013 quarterfinal, when Tsonga blew out Federer in three sets. Another telling number: Federer has now lost in straight sets in three of his past nine majors.
In extremely breezy conditions on Court Suzanne Lenglen, Federer never looked comfortable. He hit a number of crazily shanked shots. It was the first time Federer played a Grand Slam match without breaking an opponent's serve even once -- since 2002.
Wawrinka got an early break in the first set and made it stand up. He broke Federer again in the seventh game of the second set with four overpowering forehands. The last induced Federer to push a weak forehand volley into the net.
There was an uncharacteristic visit from the ATP trainer in the sixth game of the second set; he applied a Band-Aid to the second finger on Federer's right hand for an apparent blister. But as so often happens, a Band-Aid can't stop the hemorrhaging when the wound is fatal.
Federer had come back nine times from a 2-0 deficit, but not this time.
The third-set tiebreaker was 3-all when a controversial call changed the complexion of the frame. Wawrinka ripped a forehand close to the line that was called out, but umpire Kader Nouni got down out of his chair, inspected the mark and deemed the ball in. It was Nouni who made another charged call in the third-round match between Serena Williams and Victoria Azarenka, a decision favorable to Williams that left Azarenka calling it "bulls---."
"I guess I would have to see it again on replay," Federer said. "I hope it wasn't a mistake. And if it was, you know, it was obviously a costly one and a big one for me. But it really doesn't matter how he hit the shot if I was going to miss it anyway.
"There was a call, and as I'm hitting it, does it throw you off or not? I don't know. But that's the rules of the game, that if it was during the shot just before that it's being replayed. I hope it was after, for the sake of it. But if not, clearly it's a tough one."
That gave Wawrinka a 5-3 lead, which he consolidated with a terrific forehand down the line with Federer nearly off the court. The match-winning shot was an easy forehand volley into an open court.
"Of course you're disappointed when you lose," Federer said. "Being a tennis player, losing, I don't know about you, but it's like writing a paper, which is a very poor well, to say the least a very poor paper.
"And then everybody is going to kill you afterwards. It's the same when you lose one. You know, I would say there is nothing really pleasant in losing. So, yeah, no, it's a pity. It's a pity I couldn't do better than that. That's what I thought immediately."
As Federer walked off the court to applause, the sun was setting. There might be a metaphor in there somewhere.