Roger Federer has vowed to return to Wimbledon next year but said he felt "just awful" after a shock five-set defeat to Kevin Anderson on Wednesday.
A marathon quarter-final lasting four hours and 13 minutes ended with defending champion and eight-time winner Federer, who had a match point in the third set, losing 13-11 in the fifth.
Federer, 36, said: "Of course the goal is to come back here next year. I wouldn't call it 'unfinished business'. I felt like I did some good business here in the past already."
He added: "It's disappointing losing the next two sets after winning the first two and having match points. I've been there before. I know what kind of energy I need to bring to the fifth. I was able to bring that.
"To be honest, I didn't feel mental fatigue. Now I feel horribly fatigued and just awful. It's just terrible. But that's how it goes. Credit to him."
An inspired Anderson was relentless, thudding serves and eventually overpowering the 20-time Grand Slam winner to end his bid for a ninth title with a 2-6 6-7 (5-7) 7-5 6-4 13-11 win.
"Sometimes you don't feel good, and you try your best," added Federer.
"It's just not one of my best days, but they don't happen very often either. It's one of those average days when you have to try to win the match, and I just couldn't get it done."
A jubilant Anderson, US Open runner-up last year, celebrated his first win over Federer in five attempts and a maiden appearance in a Wimbledon semi-final.
The 32-year-old South African, seeded eighth, said: "I feel the few times I've played him in the past, I've walked onto the court without the necessary belief that I needed to to get through the match.
"If you play somebody ranked lower than you, you have a bit more natural confidence in the match. In tough times you can sort of rely on 'hey, I feel like I'm a better tennis player, I'm going to get through'.
"I felt it was a little bit tough saying that against Roger. But I changed that phrase and said 'What's happened in the past is in the past. All I need to worry about is today.'
"I felt like I was just trying to keep myself very highly motivated, a lot of belief in myself and said 'Today is going to be my day'."
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