A dejected Roger Federer admitted he self-destructed as his decline continued with a straight-sets defeat by Tommy Robredo in the fourth round of the US Open.
Two months after he was beaten by Sergiy Stakhovsky in the second round at Wimbledon, the 17-time grand slam champion slumped to a 7-6 (7/3) 6-3 6-4 defeat against a man he had not lost to in 10 previous meetings.
The defeat continues a miserable season for the 32-year-old, who has dropped from world number one to number seven in less than 12 months and has failed to reach a grand slam final for the first time since 2002.
It also means there will be no first meeting at Flushing Meadows between Federer and Rafael Nadal, who were seeded to meet in the quarter-finals.
Federer said: "I kind of feel like I beat myself, without taking any credit away from Tommy. Clearly he was making sure he was making many balls. It was up to me to make the difference and I couldn't.
"I kind of self-destructed, which is very disappointing, especially on a quicker court. Your serve helps you out. You're going to make the difference somewhere.
"I just couldn't do it. It was a frustrating performance."
With the humidity level at 91%, perhaps it was not surprising that Federer never looked comfortable.
He was not moving well, tactically he was suspect and 43 errors in three sets betrayed an understandable lack of confidence.
The statistic that really hurt the Swiss was only two break points won from 16 chances, and Robredo made sure he played the solid match his opponent tried desperately to find but could not.
Federer twice fought back from a break down in the opening set but lost five straight points to end the tie-break.
Robredo, who is less than a year Federer's junior, had only won three sets in all their previous meetings and never the opening one.
When the 19th seed took the second set as well, the packed crowd on Louis Armstrong knew Federer was in deep trouble, and a break in the seventh game of the third set was enough for Robredo to clinch one of the wins of his life.
Federer had looked utterly untroubled in the first three rounds and he remains convinced he can find his best form again.
"It just ended up being a bad combination of many things," he said.
"So I've definitely got to go back to work and come back stronger, get rid of this loss now as quick as I can, forget about it, because that's not how I want to play from here on.
"I want to play better. I know I can. I showed it the last few weeks, that there is that level. So today was pretty frustrating."
The match was moved from Arthur Ashe to Armstrong not long before the start because of a lengthy rain delay.
The two courts evidently do play very differently, with Andy Murray one player who struggles to play anything like his best on Armstrong.
It was the first time Federer had played a match on Flushing Meadows' second court for seven years, but he insisted that was not a mitigating factor.
"That should not be the issue," he said. "That's definitely the last excuse you could find.
"I've been practising on Armstrong. I was prepared for it. I was even happy about it. I thought it was going to be a great atmosphere, that I could take advantage of maybe the fact that people were really going to get behind me."
The 32-year-old had talked at the start of the tournament about how much he wanted to play Nadal for the first time in New York, but that was not chief among his regrets.
"It would have been the quarters, not a final," he said. "It's not that much of a disappointment at the end of the day. If I'm playing like this, I'm not going to beat Rafa, or (his fourth round opponent Philipp) Kohlschreiber for that matter."
At the same time on Saturday night Robredo had been fighting to avoid being taken to a deciding set by British qualifier Dan Evans, although the fact the match was also on Armstrong may have been some help.
It has been a superb year for the Spaniard, who was ranked 471st when he came back from thigh surgery last spring.
He said: "It's amazing. For me, Roger for the moment is the best player of all time. And to beat him in a huge stadium like the US Open and in a match of best-of-five sets, it's like a dream.
"I am so, so happy. I am in the quarter-finals again. It was a great day."
Also through to the last eight is fourth seed David Ferrer, who survived a tough encounter against Janko Tipsarevic to win 7-6 (7/2) 3-6 7-5 7-6 (7/3).
Tipsarevic served for both the first and third sets but was left to rue missed opportunities.
Ferrer has struggled for form this summer but his consistency at the grand slams has been hugely impressive, and this win made it nine consecutive quarter-finals or better.