Rome, May 17 (IANS) Romanian tennis player Simona Halep, world No. 1, on Thursday advanced to the quarterfinals of the Italian Open, a WTA clay court tournament held in Rome, as American Madison Keys had to retire with a right rib injury.

The 2017 Italian Open finalist is set to play either France's Caroline Garcia or American Sloane Stephens, reports Efe.

"I am really sorry I have to withdraw from this year's Internazionali BNL d'Italia," Keys said in a statement. "I felt my rib in my match yesterday and after trying to warm up this morning it will still painful. I look forward to returning to this great event next year and seeing all my fans in Rome."

Halep had started her 2018 Italian Open campaign on Wednesday by routing Japanese Naomi Osaka 6-1, 6-0.

The 26-year-old Halep seeks her seventh clay court title, following the Hungarian Open, Nuremberg Cup (2013), Bucharest Open (2014, 2016) and Madrid Open (2016, 2017).