LINZ, Austria -- American teenager Coco Gauff notched a big upset over World No.8 Kiki Bertens of the Netherlands, 7-6(1), 6-4 on Friday to move into her first-ever WTA semifinal at the Upper Austria Ladies Linz.

The 15-year-old has experienced a huge change of fortune during the week, going from losing in the final round of qualifying to entering the main draw as a lucky loser and attaining the first Top 10 victory of her career with her 97-minute victory over top-seeded Bertens.

"It was definitely crazy," Gauff told the press, after her massive victory. "Today was my first Top 10 win, so I’m super proud of myself for that. It was a good match, Kiki played great, and obviously I couldn’t ask for anything better so far in this tournament."

Read more: Luxembourg 2019: Gauff & McNally into main draw

Very little separated the two players, with a single break of serve in the encounter determining the victor. Gauff staved off both of the break points she faced in the tilt, won three-quarters of her first-service points, and claimed half of the points off of Bertens's second serve.

"I wasn’t really too nervous until the match points came along," stated Gauff. "I should be the opposite! But it’s okay, I’m glad that I got through it. "

"I guess [Linz is] my little lucky place," Gauff added. "I didn’t know what to expect coming here, and I’m glad I was able to take the best of the opportunity. I got in as a lucky loser and I’m in the semis, so I hope I can keep this going."

Gauff exhibited exceptional prowess in the forecourt as the match commenced, punching victorious volleys and delivering divine dropshots, but the thunderous power game of Bertens kept her on level footing as she blasted her way through any moments of peril in the early going.

Bertens had to grit her way through a tough service game to hold for 4-4, as she double faulted to give Gauff the first break point of the match. But a strong serve by the Dutchwoman erased that chance, and she continued to find robust deliveries which pulled her through the game, as the combatants continued to stay deadlocked throughout the opening frame.

Despite an evenly-matched run to 6-6 with zero breaks of serve, Gauff quickly turned the pivotal first-set tiebreak fully in her favor. After opening the breaker by winning a scintillating rally with a drop volley winner, the American stayed steely as a run of unforced errors came from the racquet of Bertens.

The Dutchwoman hit her third double fault of the set to cede a 5-1 lead to Gauff at the changeover, and after another wide forehand by Bertens, the teenager reached 6-1 and held five set points. Gauff only needed one, ending the set with a forehand winner and putting her on the precipice of a signature upset.

In the second set, Bertens had an early opportunity to pull ahead, firing a forehand winner to queue up a break point for a 2-0 lead. Gauff, however, had other ideas, as she executed a drop volley to force an error and pull herself out of danger, eventually moving to a hold for 1-1.

Gauff was immediately rewarded in the next game as Bertens misfired on forehands, as the American suddenly attained the first -- and what would prove to be the only -- service break of the match. Bertens never faltered on serve after that, but the Dutchwoman got no further looks on Gauff’s serve, and the teenager would go on to close out the victory on her second match point.

Gauff will now take on former Top 10 player Andrea Petkovic of Germany for a spot in her first-ever WTA singles final. Petkovic dispatched Slovakia’s Viktoria Kuzmova, 6-4, 6-1, to book a ticket into her first WTA semifinal of the 2019 season.