LINZ, Austria -- The rapid rise of Coco Gauff in 2019 has hit another massive milestone, as the American teenage sensation won her first WTA singles title at the Upper Austria Ladies Linz, outlasting former Top 5 player Jelena Ostapenko of Latvia, 6-3, 1-6, 6-2, in the championship match on Sunday.

"I’m still overwhelmed and shocked," the singles champion told the press, after her victory. "I guess it’s crazy to say it’s my first WTA title. This was definitely not on the calendar at the beginning of the year, because I didn’t think I’d have a chance to get in, and now I’m the champion, so it’s crazy."

It is a stunning conclusion to an already noteworthy week for Gauff, who went from losing in the final round of qualifying to entering the main draw as a lucky loser and claiming her first-ever Top 10 win over Kiki Bertens in her maiden WTA quarterfinal.

The young American went on to reach her first tour-level semifinal and final before her 99-minute win over Ostapenko gave her the trophy. Already guaranteed to make her Top 100 debut after her first couple of wins this week, Gauff is projected to rise inside the Top 75 in the WTA rankings on Monday.

"It’s just literally insane that I got in as a lucky loser and now I’m the champion," Gauff said.

"My dad told me when I got in, before the first main-draw match, he said ‘You can’t lose twice in the same tournament!’" Gauff continued. "I’m sure he never thought it would come this far, to being the champion, but I guess he was right!"

15-year-old Gauff, who started the season ranked well outside the Top 600, becomes the youngest WTA singles titlist since Nicole Vaidisova of the Czech Republic picked up titles at Vancouver and Tashkent by the age of 15 years, 5 months in 2004.

Gauff also becomes the second player in the last two seasons to claim a debut WTA singles title as a lucky loser, matching the feat of fellow teenager Olga Danilovic, who was a lucky loser when she hoisted the trophy at the Moscow River Cup last season.

The American already has plans for some of her prize money from her first singles title. "I know Halloween is coming up, and it’s one of my favorite times of year, so I guess I’ll splurge a little bit on my costume and make sure it’s right," said Gauff.

Her costume will remain "a secret, because I know last year they had a WTA contest for the best costumes, and I came in third [place]. This year my goal is to come in first!"

Gauff took the early lead in the match after fending off two break points in her opening service game. The American notched a break for a 2-0 lead, using great depth of shot to draw errors from Ostapenko, and she consolidated by slamming an ace to reach 3-0.

Ostapenko began to find her range on her powerful groundstrokes, getting on the board for 3-1 after a wicked backhand down the line, but the Latvian could not garner any more break points in the set as Gauff served well and used dropshots with aplomb. The American teen reached set point at 5-3 with an ace, and she drew an error with a deep backhand slice to seal the opener.

However, the script was flipped in the second set. Ostapenko had to save a break point in the first game of that frame with an error-forcing forehand down the line, but after that, the 2017 Roland Garros champion began to find her targets with her rocket shots more frequently. She took advantage of a lapse by Gauff, breaking the American for the first time, at love, to lead 2-0.

Gauff pulled back on serve in the next game, but Ostapenko reclaimed her break advantage to lead 3-1 after a winning volley. Ostapenko maintained her dominance in the second set with aggressive play inside the margins, earning another break with multiple winners to lead 5-1. The Latvian converted her first set point in the next game with an ace, and the match was level.

"In the second set, Jelena started coming up really fast, hitting the ball really fast, hitting winners, and there was not much I could do," Gauff admitted.

The third set, though, swung back in Gauff's favor, as she garnered a quick break to lead 2-0 after a backhand off the baseline forced an error from Ostapenko on break point. Gauff started to cruise from there, blasting big returns to earn a second break for 4-0.

At 5-0, Gauff held two match points, but the Ostapenko ground game started to get back into rhythm, and the fiery Latvian held on for 5-1. The former World No.5 began to find her targets once again, and she broke Gauff at love to reach 5-2, hoping to earn a comeback win after saving match points, as she had in Saturday’s semifinals.

Gauff, however, regrouped in the next game, earning a third match point following a netted backhand by Ostapenko. The third time, in fact, was the charm for the teenager, as Ostapenko fired a forehand just long, and Gauff joined the roll of WTA singles titlists.

"I started off the third set really strong," Gauff concluded. "It’s been an unbelievable week for me."