Lauren Davis won a near three-hour clash over Grace Min on Monday, to earn herself a clash with top seed Eugenie Bouchard at the Family Circle Cup.
Davis edged Min 6-7 (1-7) 7-6 (7-2) 6-3 in a momentum-shifting affair, winning in two hours, 53 minutes at the WTA Premier event in Charleston, United States.
Min won the first set despite Davis having the chance to serve for it in the 10th game, before the roles reversed in the second set - Min blowing a chance to serve for the match in the 12th game, before Davis squared the contest.
There were only three service holds in nine games in the decider as both players endured trouble, but Davis' breaking of Min four times in succession from 1-1 was the difference.
Davis has met fellow 21-year-old Bouchard once before, the Canadian prevailing in straight sets at the Australian Open in 2014.
Seeds Zarina Diyas (11th) and Heather Watson (16th) both bowed out in the first round of the green-clay event.
Diyas was outplayed by qualifier Lucie Hradecka 4-6 6-1 6-3, while Watson fell to Donna Vekic 6-3 4-6 7-5.
Mona Barthel, the 15th seed, progressed with a 6-3 6-3 result against Timea Babos, while 13th seed Irina-Camelia Begu got past qualifier Laura Siegemund 6-2 7-6 (7-5).
Ajla Tomljanovic took over two-and-a-half hours to advance past Alexandra Dulgheru 7-6 (7-5) 4-6 6-4.
There were mixed results for the locals with Shelby Rogers and Sachia Vickery winning, but their fellow Americans Jessica Pegula, Irina Falconi, Christina McHale, Nicole Gibbs and Alison Riske bowed out.
Wildcard Vickery downed qualifier Pegula 4-6 6-3 7-6 (7-4), while Rogers thrashed Silvia Soler-Espinosa 6-3 6-1.
Falconi lost to Tatjana Maria 6-1 6-3, McHale was mastered by qualifier Danka Kovinic 6-2 6-3, and Gibbs was no match for Zhang Shuai 6-4 7-5.
Zhang will take on second seed Ekaterina Makarova in the last 32.
Kateryna Bondarenko triumphed over Riske 6-4 4-6 6-1.
Yaroslava Shvedova defeated Stefanie Voegele 7-5 6-2, but her fellow Kazakh Yulia Putintseva was not as fortunate - losing to Evgeniya Rodina 6-3 6-3.
Chanelle Scheepers saw off Marina Erakovic 6-2 2-6 6-4, and qualifier Kristina Kucova fought past Mirjana Lucic-Baroni 6-3 3-6 6-3.