American tennis star, 15, seals stunning 14-year first

Cori Gauff has reached her first WTA quarter-final after Kateryna Kozlova retired during the third set of their second-round match at the Linz Open.

The 15-year-old prodigy announced herself to the tennis world at Wimbledon earlier in the year after stunning five-time champion Venus Williams in her debut appearance.

Gauff trailed by a set and a break but was on the verge of a comeback when Kozlova retired with the American teenager leading 4-6 6-4 2-0 in Austria on Wednesday.

At 15 years and 214 days, Gauff became the youngest player to reach a WTA quarter-final since January 2005, when Sesil Karatancheva did it aged 15 years and 153 days.

"It's a good accomplishment, and hopefully I can continue to push that to the semifinals," Gauff said.

Cori Gauff has broken into the top 100 after reaching her first WTA quarter-final. Pic: Getty

"I guess that I'm used to being the youngest to do a lot of things, and I hope that I can continue to do that and enjoy my youth years, because as everyone tells me, it doesn't last long."

Gauff's milestone moment also saw the teen phenomenon break into the top 100 of women's tennis for the first time in her career.

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The American is playing in her first tournament since losing to Naomi Osaka in the third round of the US Open and only made the main draw in Linz as a "lucky loser" after losing in qualifying.

She beat Stefanie Voegele in straight sets in her opening match on Tuesday at the indoor tournament.

"I just want to continue to use these matches to improve. My dad told me he saw improvements even since the US Open," Gauff said.

"Right now, it's all about matches for me, and getting more matches under my belt, as much as possible. I feel fresh and eager to do well."

Gauff had her major breakthrough at Wimbledon this year where she reached the fourth round, but had never won a tour-level match indoors before this week.

Top-seeded Kiki Bertens advanced to the second round by beating Masaki Doi of Japan 6-4 7-5, while No. 8 Ekaterina Alexandrova defeated Kristyna Pliskova 3-6 6-0 6-1.

Bertens next faces Alison Van Uytvanck of Belgium and would play Gauff in the quarter-finals if she advances.