Roger Federer said 'time was ticking' in his battle to recover form and fitness for the French Open after losing to rising Austrian Dominic Thiem 7-6 (2) 6-4 in the third round of the Italian Open yesterday.

The former world number one still looks short of his best after knee and back injuries and struggled to get to grips with the 22-year-old Thiem at the Foro Italico.

Thiem, ranked 15th, recovered from an early break and streaked into a 6-2 lead in the tiebreak before taking the opening set with a backhand winner.

He broke 34-year-old Federer's serve again midway through the second set as he claimed the 32nd victory of a breakthrough season that saw him rise to a career-high 13th.

Seventeen-times major champion Federer shrugged off the defeat, saying his immediate priority was the French Open that begins on May 22.

"This is like, 'who cares about the results here?'. It matters what comes now in the next couple of months," Federer told a news conference.

Federer, a four-times finalist in Rome, missed last week's Madrid Open with a back problem but said there had been some encouraging signs this week.

While on the women's front, top seed Serena Williams enjoyed a 7-6 (7) 6-1 victory over fellow American Christina McHale while third seed Garbine Muguruza of Spain also reached the quarter-finals by beating Latvian Jelena Ostapenko.