Tenth seed Victoria Azarenka suffered a shock straight-sets defeat by world number 161 Anna Karolina Schmiedlova in the French Open second round.
The Belarusian, 31, reached the US Open final earlier this month but struggled on the clay against Schmiedlova, who won 6-2 6-2.
The Slovak fell in the second set and the trainer was needed to treat her knee, but it did not halt her progress.
Earlier, third seed Elina Svitolina beat Mexican qualifier Renata Zarazua.
The Ukrainian, 26, failed to win a game in the second set but recovered to claim a 6-3 0-6 6-2 victory.
“I was trying to get back into the match,” she said. “I lost my way a bit and was making too many errors.”
Svitolina won her 15th WTA title in Strasbourg last week but is yet to reach a Grand Slam final.
She will face Russian world number 31 Ekaterina Alexandrova next.