LINZ, Austria - American teenager Coco Gauff sealed a place in her first WTA quarterfinal at the Upper Austria Ladies' Linz on Wednesday when Ukrainian Kateryna Kozlova retired in the final set of their second round match with a left lower leg injury. 

After getting into the main draw following the withdrawal of No.6 seed Maria Sakkari, Gauff beat Stefanie Voegele on Tuesday on what she called her "lucky day," but needed to use all of her skills to battle back against the Ukrainian No.4 on Centre Court.

Read more: 'Today was my lucky day' - Gauff vanquishes Voegele in second shot at Linz

From a set and a break down at 6-4, 3-2, Gauff won four of the next five games to force a final set, and claimed eight of the first nine points of the decider before Kozlova could no longer continue, with the scoreboard reading 4-6, 6-4, 2-0 in favor of the 15-year-old. 

"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 as more matches under my belt, as much as possible. I feel fresh and eager to do well."

At 15 years and 214 days, Gauff is the youngest player to reach the quarterfinals at a WTA event in nearly 15 years.

The streak dates back to January of 2005, when Sesil Karatancheva advanced to the last eight as a qualifier at the Gold Coast at 15 years and 153 days.

"I know her, oh wow," a surprised Gauff told reporters when they informed her of the feat. "It's a good accomplishment, and hopefully I can continue to push that to the semifinals.

"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." 

Looking to keep her deepest-ever run at a tour-level tournament to date alive, the lucky loser will have to wait to learn her next opponent.

In the last eight, she could face top seed Kiki Bertens, who is still in contention to qualify for the Shiseido WTA Finals Shenzhen and begins her tournament against qualifier Misaki Doi later on Wednesday, or recent Tashkent Open champion Alison van Uytvanck.

With the victory, Gauff is projected to break the Top 100 in the WTA rankings on Monday, and can confirm and improve her standing based on other results.

"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," she said.

"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. 

"A lot of my points came from the Slams and this tournament really pushed me inside, and it's crazy because I'm a lucky loser...and now that this has happened, I hope to get as high as possible.

"I don't really think too much about ranking, but you have to have some stepping stones to reach for."