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, while Iga Swiatek cruised into the women's semi-finals.
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, 28, 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.
World number one Swiatek continued her bid for a third Rome title in imperious style, strolling into the last four past Madison Keys 6-1, 6-3.
"Today I'm really proud of myself because I feel like I'm playing better and for sure this was the best day for me in Rome," said Swiatek.
In the last four Swiatek will face her toughest test yet in third seed Coco Gauff, who beat Zheng Qinwen 7-6 (7/4), 6-1 in the day's final match on centre court.
She maintained her red-hot form at the Foro Italico, where she has not yet dropped a set, ahead of her French Open title defence later this month.
The three-time Roland Garros champion arrived in Rome off the back of winning a third WTA 1000 title of the season in Madrid.
And she could yet become the first woman since Serena Williams in 2013 to win in the Spanish and Italian capitals in the same season.
Alejandro Tabilo's fairytale continued after stunning 24-time Grand Slam champion Djokovic, reaching the quarter-finals by winning a hugely entertaining battle with Karen Khachanov, 7-6 (7/5), 7-6 (12/10).
Tabilo reached the last eight of a Masters 1000 event for the first time and will next play China's Zhang Zhizhen.
"Just being in my first quarter-final is an unreal feeling, just trying to soak it all in right now. It's a crazy feeling," said Tabilo.
"With the win two days ago it's been crazy. I just had to turn off the phone and just kind of be with the team, be with the people close to me and I'm just happy that I was able to refresh the mind."
The 26-year-old had a much harder time of it against 18th-ranked Khachanov, whose six tour titles have all come on hard courts, than against Djokovic.
Tabilo came through a thrilling second-set tie-break which featured 11 service breaks, two set points for Khachanov and five match points, exploding with joy after the winning volley.
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