Roger Federer was knocked out of Wimbledon in an epic five-setter
Anderson produced one of the great Wimbledon comebacks on No 1 Court, saving a match point in the third set before going on to take an epic 2-6, 6-7, 7-5, 6-4, 13-11 victory.
And while 36-year-old Federer insisted he “felt good” going into the final set, there was no hiding from how he felt afterwards.
“Now I feel horribly fatigued and just awful,” Federer said.
“It’s just terrible. But that’s how it goes, you know. Credit to him.”
He added: “You don’t want to be on the loser’s side.
“It motivates me to do extremely well here because I don’t want to sit here and explain my loss.
“That’s the worst feeling you can have as a tennis player.”
Federer had been installed as the No 1 seed and was a short-odds pre-tournament favourite to defend his title successfully.
Kevin Anderson pulled off a remarkable win against Roger Federer
But Rafael Nadal will now be the front-runner to claim his third trophy at SW19, assuming he makes it through his own big-serving challenge in the quarter-finals against Juan Martin del Potro.
And his great rival Federer, despite the fact he will be 37 when the next Wimbledon comes around, allayed any fears that he might hang up his racket sooner rather than later.
“I think I just love being around here. It’s a good vibe,” Federer said.
“We have a good time as a family.
“I have great memories from here. My heroes all won here. Every time I come back here, I try to be like them, so it’s nice to be here.
“I don’t know how long it’s going to take me [to get over losing]. Might take me a while. Might take me half an hour. I have no idea what it’s going to be.
“Of course, the goal is to come back here next year.
“But I wouldn’t call it ‘unfinished business’. I felt like I did some good business here in the past already (smiling).
“So I’m all right. Just disappointed now.”