American teenage star Coco Gauff beat off a stiff challenge from No 2 seed Aryna Sabalenka to make it through to the quarter-finals at the Top Seed Open in Lexington, Kentucky.
Gauff prevailed 7-6 (4) 4-6 6-4 in a match that lasted nearly three hours.
The American was broken seven times and appeared frustrated at tines before she found her game to eventually see off the Belarusian.
The win, which will see Gauff enter the world top 50 rankings.
Earlier, eighth seed Ons Jabeur shook off qualifier Olga Govortsova to book her place in the quarter-finals, winning 3-6 6-2 6-4.
Czech Marie Bouzkova saw off 21-year-old Russian Ana Blinkova 6-4 6-2 in the other last 16 clash in Kentucky.
Krystina Pliskova dismissed second seed Petra Martic 6-1 7-5 to deliver the biggest shock yet at the Prague Open.