Fourth seed Dominic Thiem joined eighth seed Stefanos Tsitsipas and ninth-ranked Karen Khachanov in exiting the US Open at Flushing Meadows on Tuesday.

Austrian 25-year-old Thiem, twice a French Open runner-up, lost 6-4 3-6 6-3 6-2 to unseeded Italian Thomas Fabbiano, with 48 unforced errors proving too much to overcome. Meanwhile Greek 21-year-old Tsitsipas, tipped as a future Grand Slam champion when he beat Roger Federer last year, lost 6-4 6-7 (5-7) 7-6 (9-7) 7-5 to Andrey Rublev.

Russian Khachanov, a quarter-finalist at the French Open back in June, failed to convert nine break points and was beaten 4-6 7-5 7-5 4-6 6-3 by Canadian Vasek Pospisil. Tsitsipas suffered from cramp during his defeat to Rublev and the youngster admitted to suffering from mental fatigue in the Bronx.

“I feel like I’m doing the same thing over and over again, and my brain can’t really take it anymore,” he said. “I feel like I’m doing the same routines on the court, the same execution, the same strategies.” Tsitsipas also became irritated with umpire Damian Dumusois, who docked the Greek a point for a time violation in his exit.

He feels the official has ‘something against’ him. “The umpire was very incorrect in what he was telling me during the match. He has something against me. I don’t know why,” he added. Rublev stunned Federer last month at Cincinnati Masters and the 21-year-old was delighted to come through another tough assignment.

“We played an amazing match. It was tough conditions for both of us. He started to cramp. I know what it’s like; I was cramping too and tried not to show it. But this is amazing, winning matches like this gives you confidence,” he said. Rublev is 81.00 to win the US Open.