Fran Jones stunned a player ranked 152 places above her and fellow Briton Ryan Peniston ended an eight-match losing streak in French Open qualifying.
Jones, 22, knocked out American Coco Vandeweghe 6-3 6-3, while Peniston beat Turkey's Altug Celikbilek 6-4 6-2 to reach the second round in Paris.
They need to come through two more rounds to reach the main draw of the Grand Slam, which starts on Sunday.
Compatriot Sonay Kartal lost her match, despite having led 6-2 5-1.
Having been on the brink of victory, she lost six games in a row to fall 2-6 7-5 6-4 to Viktoria Hruncakova.
World number 316 Jones has returned to form this year after an injury-hit 2022, and her victory over two-time Grand Slam semi-finalist Vandeweghe was well deserved after a dominant performance.
More Britons will seek to join her in the next round of women's qualifying, with Harriet Dart, Heather Watson, Katie Boulter, Lily Miyazaki and Katie Swan all in action on Tuesday.
Liam Broady and Jan Choinski begin their qualifying campaigns on Tuesday as they, along with Peniston, seek to join Britons Cameron Norrie, Dan Evans, Kyle Edmund and Jack Draper in the Roland Garros main draw.
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