Jo-Wilfried Tsonga was at a loss to explain what went wrong after he suffered his earliest Grand Slam exit in five years at the US Open on Thursday.
The fifth seed was out of sorts as he was beaten 6-4, 1-6, 6-1, 6-3 by Slovakian Martin Klizan in the second round. Tsonga said he was fully fit and healthy but that for some unknown reason he could not find his best form when he needed it.
"I'm not very satisfied," Tsonga said. "I lost second round. I'm used to playing the round of 16 or quarter-finals, sometimes semis.
"(But) it's tennis. Today I didn't play my best tennis and my opponent was better than me the whole match I think, and that's it."
It looked like normal service had been restored when Tsonga won the second set easily but just as quickly, his game disappeared again.
World No 52 Klizan had never advanced beyond the second round at a grand slam event before but the left-hander surprised Tsonga with some inspired tennis.
In a late-night thriller, seven-time Grand Slam champion Venus Williams made her second consecutive US Open second-round exit as German sixth seed Angelique Kerber ousted the American 6-2, 5-7, 7-5.
The loss made this the first year in Williams' pro career, which began in 1997, that she has not gone past the second round in any major tournament.
"Losing a match like this isn't a lot of fun, but that's sport," Williams said. "All I had was fight because I didn't play well."
Kerber, a left-hander who advanced to the semifinals at Wimbledon and at last year's US Open, set up a a third-round date with Olga Govortsova.