Injured and aching Rafal Nadal limped out of the Cincinnati Masters in the third round on Thursday a 6-1, 6-3 victim of teenaged Borna Coric.
The listless performance - among the heaviest defeats of Nadal's career - was punctuated by a visit from the trainer after the opening set. It was in sharp contrast to the Spaniard's gold-medal doubles success last weekend at the Rio Games.
In other major losses, Nadal was beaten in 2008 by Mikhail Youzhny in the Chennai final 6-0, 6-1 and went down in the Doha final last January to Novak Djokovic 6-1, 6-2.
"After two months and a half and with an injury in the wrist, the normal thing is try to come back a little bit slower," Nadal said.
He said he was "at the limit" after Rio and it was clear he was not ready, but "it was not easy to take the decision to not come here after the Olympics."
He added: "I didn't want to be back home. I spent enough time there the last three months. I needed to keep practising, keep playing."
Nadal was bothered by a left elbow injury and a too-tight strapping on his left ankle. The 30-year-old missed two months with a left wrist injury and was playing his first Tour event since the French Open.
Nadal had trouble mustering energy in the 72-minute upset loss to Coric as Olympic fatigue seemed to catch up with him.
At one point the 19-year-old Coric, ranked 49th, won 10 games in a row to take the opening set and grab a 4-0 lead in the second,
The youngster's upset was his second career victory over a top five player (he beat Andy Murray in 2015 at Dubai) and ended a 10-match loss streak to the top 10 elite.
"It was an unbelievable match from my side," Coric, playing in his first Masters 1000 quarter-final, said. "I played well from the beginning and he was not playing his best tennis.
"I served well and was hoping for some aces (he got eight). That's what saved me."
Nadal now has 11 days to recover and prepare for the US Open after missing two summer months of play since quitting Roland Garros with a left wrist injury.
Second seed Stan Wawrinka also crashed out in straight sets, losing to this week's doubles partner Grigor Dimitrov 6-4, 6-4.
Wawrinka skipped Rio with back pain but said his fitness has not been an issue for a week or more.
The Swiss produced 28 unforced errors in the loss lasting for less than 90 minutes.
"I was fighting more the first set. I think I was very persistent in my service game. I knew that Stan will just come out and play good tennis," Dimitrov said. .
"I think early on he really did. After an early break I felt like I got into his head and into his rhythm pretty well. I started moving the ball good and hitting my spots. That just helped me today."
Australian Bernard Tomic upst Japan's fifth seed Kei Nishikori 7-6 (7-1), 7-6 (7-5).
Steve Johnson took the top American ranking from John Isner through a knockout of seventh seed Jo-Wilfried Tsonga 6-3, 7-6 (8-6). Austrian eighth seed Dominic Thiem advance don a walkover when Gael Monfils withdrew with back pain.
In the women's third round, second seed Angelique Kerber moved a step closer to taking the WTA number one ranking as she beat Barbora Strycova 7-6 (7-5), 6-4.
Rio silver medallist Kerber could take over the top of the table form Serena Williams if she can win the weekend Cincinnati title
Third seed Simona Halep, 2015 runner-up, went quietly about her business with a 6-1, 6-2 defeat of Australian Daria Gavrilova.
Spain's ninth seed Carla Suarez Navarro beat US Open finalist Roberta Vinci 6-1, 7-5. 15th seed Karolina Pliskova eliminated Japan's Misaki Doi 7-5, 6-3.