Eighth seed Petra Kvitova came back from a set down to beat Veronica Cepede Royg 3-6 6-1 7-5 and reach the French Open second round.
The Czech, among the title favourites, made 17 unforced errors in the first set before finding her rhythm.
Second seed Caroline Wozniacki was also tested in her first set before running away with the next in a 7-6 (7-2) 6-1 win over American Danielle Collins.
Ex-world number one Victoria Azarenka lost 7-5 7-5 to Katerina Siniakova.
“Even though I am doing good things in practice, I’m not able to transfer it to the match,” said Belarusian Azarenka, whose season has been disrupted by a custody dispute over her young son which has led to her withdrawing from tournaments.
Kvitova, who suffered career-threatening injuries to her playing hand in a knife attack in 2016, looked in danger of following Azarenka out of the door at Roland Garros against world number 87 Cepede Royg.
Trailing 5-4 in the third set against the Paraguayan and 0-15 on her serve, Kvitova delivered three successive aces to keep herself in the match before breaking in the next game and then serving out the match.
“It was really tough, we played over two hours. I was more relaxed in the second but the third was tough again and I was lucky that I got the break,” said two-time Wimbledon champion Kvitova, who next faces Spanish qualifier Lara Arruabarrena-Vecino, who beat Hungary’s Timea Babos 7-6 (7-5) 6-3.
Meanwhile, Japan’s Naomi Osaka, who won this year’s Indian Wells title, beat American Sofia Kenin 6-2 7-5 to progress.