The French number one was troubled throughout her opener with Jennifer Brady and needed treatment on court before edging a final-set thriller - Mladenovic winning 9-7 in the decider.

Clay has been good for Mladenovic in 2017 with final appearances in Stuttgart and Madrid, and many saw her as France's best hope of a champion given the openness of the women's draw.

An "unlucky" accident on Sunday triggered a bad back and despite medication that continued to trouble her on Court Philippe Chatrier.

The 13th seed managed to block out the pain but expects to be troubled by it in her preparations for a second-round match with Sara Errani - who beat Misaki Doi 7-6 (9-7) 6-1.

"My back feels so-so," she told a media conference. "[An] unlucky thing happened to me yesterday and I locked my back. I had a spasm.

"This morning it was better, but it was really bad for being at the top level of playing and especially on the serve.

"I just dug in, I really don't know how I managed that."

Muguruza enjoyed a much easier passage into round two as she came through a potentially tricky clash with 2010 Francesca Schiavone in straight sets.

With Angelique Kerber already out in Paris, Karolina Pliskova could become world number one should she reach the final and Simona Halep fails to win the trophy.

Pliskova beat Zheng Saisai 7-5 6-2 to kick off her quest for the top spot in winning style, the Czech setting up a meeting with world number 86 Ekaterina Alexandrova.

There was no joy for 2015 runner-up Lucie Safarova, though, as she was dumped out by Veronica Cepede Royg, a player ranked 58 places below her.