Radwanska appeared to be cruising into the quarter-finals as she led unseeded Bulgarian Tsvetana Pironkova 6-2, 3-0 before play was suspended on Sunday, with the tournament then suffering its first washout in 16 years on Monday.

But the Pole, who was hampered by a right wrist injury, dropped 10 straight games either side of another rain delay on Tuesday as world number 102 Pironkova extended her best run in Paris.

"It feels unbelievably great. I have no words right now, I'm so happy," said Pironkova, a former Wimbledon semi-finalist.

"It was very difficult with all the rain, we waited almost three days to finish the match. But I can't complain, it turned out great for me."

Sixth seed Halep, beaten in the 2014 final by Maria Sharapova, suffered a 7-6 (7/0), 6-3 defeat to former US Open champion Samantha Stosur of Australia.

The Romanian was 5-3 up when their contest, also held over from Sunday, resumed on Court One, but Stosur broke Halep as she tried to serve out the first set before racing through the tie-break to seize control.

Stosur, the 2010 French Open runner-up, again broke her opponent to begin the second set before clinching a quarter-final berth courtesy of a second break.

The 21st seed will face Pironkova next, with the winner of that tie playing Spain's Garbine Muguruza or 108th-ranked American Shelby Rogers for a place in the final.