ROME - Daniil Medvedev's Rome Open title defence came to an early end on Tuesday after the world number four was knocked out at the last-16 stage by Tommy Paul.
Second seed Medvedev has never successfully defended an ATP Tour crown and was well below his best, stunned in straight sets 6-1, 6-4 by American Paul who claimed his first win against the former US Open champion.
"Mentally I had to be much better. I started to calm myself down and focus on the match only at the end of the match, and it was too late," Medvedev told reporters.
"It's disappointing, to be honest. I wanted to do better here."
Paul will play Hubert Hurkacz, who knocked out Rafael Nadal earlier in the tournament, in his first Masters 1000 quarter-final on clay.
"I had a bit of training before the clay court season this year and it really helped. I'm really comfortable and I'm having fun out here," said Paul on court.
Medvedev had a great chance at the Foro Italico after a raft of stars either withdrew or were eliminated early, but instead he became the latest big name to be dumped out of the last major tournament before this month's French Open.
Rome is missing the world's top four ranked men after Novak Djokovic's exit on Sunday and Italian world number two Jannik Sinner and third-ranked Carlos Alcaraz both dropped out injured before the tournament.
Holger Rune, who lost last year's final to Medvedev, Madrid champion Andrey Rublev -- ranked sixth in the world -- and beaten finalist Felix Auger-Aliassime have also been eliminated.
Hoping to pounce is world number five and 2017 Rome winner Alexander Zverev after sweeping past unseeded Nuno Borges 6-2, 7-5 to set up a quarter-final clash with Taylor Fritz.
Reigning Monte Carlo champion Stefanos Tsitsipas meanwhile demolished Australia's Alex de Minaur 6-1, 6-2 in an hour and will play Nicolas Jarry in the last eight.