ROME (AFP) - Roger Federer's Rome Masters bid ended with a 7-6 (7/2), 6-4 third round defeat to Austrian 13th seed Dominic Thiem, as world number one Serena Williams sailed into the Italian Open quarters on Thursday.
Swiss third seed Federer, who withdrew last week from Madrid with back pain, admitted on Wednesday he had been surprised to get past second round opponent Alexander Zverev in straight sets.
Rome marks only the fourth tournament of the season for Federer, who underwent knee surgery in early February, the first operation of his career.
And amid ongoing back pain that has compounded his hopes of an 18th Grand Slam title in Paris, Federer admitted: "I actually thought I could really do a good result in Paris. Now, after the last couple of weeks, it's been more difficult.
"I see my chances as, you know, as not great."
The 17-time Grand Slam champion only decided to face Thiem at the last minute on Central Court, and the Austrian capitalised to finish off an obviously ailing Federer in 1hr 18mins.
In the quarter-finals, Thiem will now play Japan's sixth seed Kei Nishikori, who swept aside French 11th seed Richard Gasquet 6-1, 6-4.
A former four-time finalist who has never triumphed in Rome, Federer will now consider his options as he tries to regain full fitness ahead of next month's French Open at Roland Garros.
But as for competing in Rome, Federer said: "My body's just not ready... I'm not going to go into specifics, because I'm not in the mood.
Federer said he will only be able to gauge his expectations for Roland Garros over the coming fortnight.
"I'm going to have a meeting with my team, talk about options we have, stay in Rome, Paris or go back to Switzerland," he said.
"Should I rest, train, do some more physio? All that stuff needs to be discussed but I'm so happy I didn't get hurt this week.
"Happy I'm through the tournament now and can look ahead. I can pace myself. In a match you can't really pace yourself."
It could be the beginning of a Rome Masters fairytale for 22-year-old Austrian Thiem, who is approaching 30 wins for the season having secured two titles already and suffered defeat to Germany's Philipp Kohlschreiber in the final at Munich nearly a fortnight ago.
Thiem admitted: "Of course, maybe if Roger wasn't 100 per cent, maybe I wouldn't win today".
But the Austrian said it was still "very nice" to beat the big champion he started watching as a youngster.
"When he started, I was 10, 11 years old. First of all, it was already very big for me to play against him in Brisbane, and now to beat him, even that he was not 100 per cent, it's very nice for me," added Thiem.
Later, defending champion Novak Djokovic faces Brazilian Thomaz Bellucci while seven-time winner Rafael Nadal plays Australian Nick Kyrgios.
Williams, meanwhile, overcame a tight first set against compatriot and qualifier Christina McHale to prevail 7-6 (9/7), 6-1 and maintain her bid for a fourth Italian Open crown.
The American world number one is also seeking a fourth French Open title and admitted her quarter-final opponent, Svetlana Kuznetsova, who stunned 2015 finalist Carla Suarez Navarro 5-7, 7-5, 6-2, should give her a good run-out.
"I think it's great," said Williams. "Right now she's probably one of the best clay court players out there so it's the perfect opportunity for me, win or lose, leading up to Roland Garros."
