Coco Gauff reached her first WTA Tour quarter-final when Kateryna Kozlova retired in the final set of their Linz Open contest on Wednesday and could face top seed Kiki Bertens in the last eight.

Gauff, a lucky loser following Maria Sakkari's withdrawal, was leading 4-6 6-4 2-0 when her Ukrainian opponent was unable to continue due to a leg injury.

The 15-year-old American won four of the next five games from a break down at 3-2 in the second set with great fighting spirit and is set to move into the top 100 after her passage in the quarter-finals was secured.

Gauff is the youngest player to move into the last eight of a WTA event since Sesil Karatancheva back in 2005.

The teenage prodigy said: "It's been a goal of mine. In January of this year, I sent a message to my friend saying I wanted to finish Top 100, and at the time I was ranked, like, 800, so it was a far-fetched goal, but I'm glad that I was able to accomplish it.

"My other goal was to get in the main draw of two grand slams, and that happened, so I'm glad that I accomplished everything that I wanted this year."

Bertens, in contention to feature in the WTA Finals, saw off Misaki Doi 6-4 7-5 to set up a second-round meeting with Alison Van Uytvanck.

The world number eight broke twice in each set to stay in the hunt for a third title of the year as she bids to secure a place in the season-ending tournament in Shenzhen.

Andrea Petkovic won an all-German second-round match against fifth seed Julia Goerges 7-6 (7-2) 6-0, while Elena Rybakina denied Anna-Lena Friedsam a place in the quarter-finals.

Anastasia Pavlyuchenkova, Jelena Ostapenko and Ekaterina Alexandrova were first-round winners on day three.