Danielle Collins upset World No. 1 Ashleigh Barty 6-3, 6-4 to advance to the third round of the Adelaide International in Southern Australia on Wednesday.
It was her first victory over a No. 1 and her first in four matches against Barty.
"I think I was really familiar with her game after losing to her three times," Collins said. "So I certainly got some great tennis lessons out of that and have learned from it."
Collins, a 27-year-old Floridian, trailed 3-1 in the first set and 4-1 in the second set. But in each set, she broke Barty's serve twice -- helped by three double faults -- and reeled off five straight victories to claim the match.
"It's just disappointing, I think, to have two sets in a row where I went on a run of losing games," said Barty, the defending champion of the tournament in her native Australia.
Next up for Collins in the quarterfinals is Iga Swiatek of Poland, the No. 5 seed, who beat Aussie qualifier Maddison Inglis 6-1, 6-3. The French Open champion hit 26 winners and smashed four aces.
Swiatek was one of only two seeded women to advance on Wednesday. Second seed Belinda Bencic of Switzerland defeated Misaki Doi of Japan 6-1, 6-3, but three others were eliminated.
American teen Coco Gauff, a qualifier, beat sixth-seeded Petra Martic of Croatia 5-7, 6-3, 6-4. Storm Sanders of Australia, ranked No. 292 in the world, toppled seventh-seeded Yulia Putintseva of Kazakhstan 6-4, 5-7, 6-1.
Jil Teichmann of Switzerland was a straight-sets winner over Qiang Wang of China, the eighth seed, 3-6, 6-3, 6-3.
--Field Level Media