Monica Puig dumped out top seed Sara Errani at the Internationaux de Strasbourg as the 2014 champion came from a set down to claim a stunning win.
Puig made it three wins from three against the 2012 French Open finalist, progressing to the second round 4-6 6-3 6-1.
The Puerto Rican said afterwards: "I'm really pleased to get the win here in Strasbourg, and it's nice coming back as a former champion.
"Errani is a really tough competitor, and after the first set, my head could have gone down, but I kept fighting and was really pleased with the victory, especially the third set score."
Defending champion and third seed Samantha Stosur had no problems in going through on the clay, beating Lauren Davis 6-3 7-5, and eighth seed Timea Babos saw off Olga Govortsova 6-4 6-1.
Carolina Garcia hammered Kirsten Flipkens 6-1 6-2, the 10th seed winning in just under 55 minutes and her French compatriot Virginie Razzano will play Puig in the next round following a 6-3 6-3 defeat of Yaroslava Shvedova.
Zarina Diyas needed three sets to beat Shelby Rogers and Mirjana Lucic-Baroni and Kateryna Bondarenko also went the distance in wins over Wang Qiang and Heather Watson.
Pauline Parmentier defeated Zhang Shuai in straight sets but second seed Sloane Stephens and Donna Vekic will have to complete their match on Tuesday after rain and bad light prevented them from completing the contest with the scores level at a set apiece.