The 13th seed, hoping to become the first Frenchwoman to lift the Suzanne Lenglen Cup since Mary Pierce in 2000, said she hurt her back on Sunday and was not even sure she could make it on to Court Philippe Chatrier.
“I pulled my back yesterday and specialists were saying I needed 48 hours, I was almost sure I could not take it to court today,” said Mladenovic, who burst into tears after a two-hour-59-minute tussle.
“It was not the best thing obviously but I promise you I will come back and will fight until the end.”
Mladenovic surrendered her serve meekly early on and received treatment after falling 3-0 down in the opener.
She looked slightly better when back on court but still appeared to be moving slowly.
Mladenovic, among the favourites after reaching the final in Stuttgart and Madrid on clay this season, stepped up a gear in the second and managed to put her opponent, who reached the fourth round at this year’s Australian Open, on the back foot.
She moved up a break three times in the decider but seemed to choke under pressure, eventually prevailing in the 16th game when her opponent dinked a forehand into the net.