A resigned Novak Djokovic was at a loss to explain the shocking ending to his French Open title defence.
Twelve months after becoming the first man in 47 years to hold all four grand slam titles, Djokovic exited Roland Garros with a 7-6 (7/5) 6-3 6-0 loss to Dominic Thiem in the quarter-finals.
Most stunning was the manner of his collapse in the third set. Djokovic won just eight points and appeared to give up.
Eurosport commentator John McEnroe accused Djokovic of tanking, adding: "It's almost as if you can't believe what you're watching, and in a match of this magnitude."
It was the first time Djokovic has lost a set 6-0 at a grand slam since 2005 and means he will drop out of the world's top two for the first time in six years.
The 30-year-old said: " I don't expect myself to play as bad as I played in the third. I don't visualise that ever.
"It was decided I think in the first set. I tried. I lost that crucial break in the beginning of the second, and he started serving better, backing it up with the first shot. He was definitely the better player on the court.
"It was not there for me today, especially in the second part of the match. I was just unable to hit the ball well and many unforced errors."
His final tally of unforced errors was 35, with 18 winners compared to 38 for his opponent, who now faces nine-time champion Rafael Nadal.
Thiem's performance certainly should not be overlooked. The 23-year-old Austrian is one of the game's rising stars and he played with bravery and intelligence, while his one-handed backhand was the shot of the match.
But even by Djokovic's up-and-down standards since his historic and emotional victory here, this was exceptionally poor.
There was little sign of how the match would end in the first set, which was very tight and lasted 73 minutes.
Djokovic led 4-2 but gave away the break with a poor service game featuring two double faults.
Thiem then saved two set points in the 10th game before three poor backhands from Djokovic cost him the tie-break.
Once Thiem broke at the start of the second set, a Djokovic comeback never looked on the cards.
"The last couple of tournaments, I have had some great matches," Djokovic said. "It's unfortunate to finish Roland Garros the way I have done.
"I obviously always expect a lot from myself, but it's a fact that I'm not playing close to my best, and I know that.
"I love this sport. I'm motivated as any other player on the Tour. Even though I have played for many years, I still want to do well."
Djokovic is not due to play again until Wimbledon but, as well as suggesting he could play a warm-up tournament on grass, he also hinted he might take a longer break.
He said: "Trust me, I'm thinking about many things, especially in the last couple of months. I'm just trying to sense what's the best thing for me now.
"Obviously there has been a lot of changes with the team and so forth. I'm excited to work with Andre (Agassi) and the new team. At the same time, I have a responsibility to the game itself.
"We'll see. Obviously it's not an easy decision to make, but I will see how I feel after Roland Garros and then decide what to do next."
Djokovic turned to Agassi after splitting for his long-time team in April in a move he called "shock therapy".
The pair both spoke enthusiastically about the time they spent together before Agassi had to leave to fulfil prior commitments.
Agassi will make himself available to Djokovic at Wimbledon, although it remains to be seen whether the arrangement can work in the long term.
For Thiem, it was the biggest win of his career and a remarkable turnaround from their last meeting in Rome three weeks ago, when, having beaten Nadal. the world number seven managed just a single game.
Thiem had only won one set against Djokovic in five previous meetings and lost easily in the semi-finals here last year.
Asked if he was surprised by his opponent's attitude in the third set, Thiem said: "The first set was very, very long and very close.
"Then in the second set, in the beginning, I was down 0-30. I still made the game and broke him in the first service game and again broke him in his first service game in the third set.
"That's very tough. It's understandable that there is a little bit of tough things mentally coming up to him. And that's why at the end it was probably a little bit easier.
"It's great for me to be in the semi-finals again, to defend that. And of course, I think on Friday is coming the toughest opponent ever here in Roland Garros."
Nadal moved into a 10th French Open semi-final after Pablo Carreno Busta retired with an abdominal problem trailing 6-2 2-0.
The title favourite, who has gone on to lift the trophy the other nine times he has made the last four, has lost just 22 games in five matches so far.