LEXINGTON, Ky. -- American teenager Coco Gauff overcame some shaky serving Wednesday to beat No. 2 seed Aryna Sabalenka 7-6 (2), 4-6, 6-4 and reach the Top Seed Open quarterfinals with her third career victory over a top-15 opponent.
Gauff, 16, hit 10 double faults and was broken seven times.
"I guess everything was an 'A' but the serving," she said.
But she hung in there with steady baseline play against the hard-hitting Sabalenka, who had 14 double faults, including four in one game.
It was a topsy-turvy match that lasted nearly three hours and featured a bit of confusion when Gauff and her father, Cori, got into a discussion with the chair umpire about what sort of coaching is allowed under new rules the WTA recently enacted. Coaches are allowed to speak with their players during a match but must do so from their seat and only when the player is on the same side of the net.
"I think it was just a confusion on the rules," Gauff said afterward. "I didn't really understand the rules to be honest. I didn't really get clarification on the rules until after she (the chair umpire) called my previous match. I was just told the coaches can't leave their seat, so I was talking to my dad and he was talking back to me. She told me, 'You have to be discreet in your coaching.' I didn't really understand.
"I guess 'discreet' can be interpreted in different ways by different refs. To be honest, I wasn't sure of the rules, but I guess I now know you can coach, but you have to be discreet about it."
Of more concern to Gauff was the way she was starting off points in her service games. At one point, she implored herself: "I've got to make the first serves. Come on."
Gauff's plan after dropping the second set?
"Just to stay calm and composed," she said in an on-court TV interview afterward, "and making her play balls."
Sabalenka is ranked 11th, behind only No. 9 Serena Williams among the women entered in the hard-court tournament that is the first professional tennis event in the United States since the start of the coronavirus pandemic.
Gauff is No. 53 but should now return inside the top 50.
Next up for her is a match Friday against No. 8 seed Ons Jabeur, who produced 10 aces while eliminating Olga Govortsova 3-6, 6-2, 6-4. Govortsova had been seeking her first WTA quarterfinal since 2014.
The other quarterfinal on that side of the draw will be Marie Bouzkova against Jennifer Brady, who beat No. 6 seed Magda Linette 6-2, 6-3 in Wednesday's last match. Bouzkova followed up her upset of No. 3 Johanna Konta in the first round by defeating Anna Blinkova 6-4, 6-2 on Wednesday.
Thursday's second-round action will include the 31st career matchup between Williams and her older sister, Venus.
The Associated Press contributed to this report.