Gauff then entered the main singles draw as a lucky loser after injuries forced several singles main draw players to withdraw.
Then Friday in the quarterfinals, Gauff topped the top seeded and eighth ranked Kiki Bertens of the Netherlands 7-6(7-1), 6-4 to claim her first ever win over a top ten player.
Gauff mixed power and defense to take set one versus the 22 year old 2017 Roland Garros champion Ostapenko.
In the second set, Ostapenko overpowered Gauff from the baseline. The American won only 13 points in the set.
In the final set, Gauff regrouped the strike several baseline winners including an inside out crosscourt backhand return winner to break serve and lead 4-0.
Gauff held serve to go ahead 5-0.
A brief two game run from Ostapenko in which she saved two match points drew the score to 5-2.
With Ostapenko serving to stay in the match, Gauff struck a down the line forehand winner to lead 0-15.
Gauff then hit a backhand down the line return winner to reach 30 all.
Ostapenko would net a crosscourt backhand then hit an inside out down the line forehand long to end the match.
Gauff, who becomes the youngest WTA Tour tournament winner in 15 years, is projected to enter the top 75 in tomorrow’s WTA Tour rankings and is ensured a main draw entry into January’s Australian Open.
“It’s been an amazing week,” Gauff said after the match.
“I hope to come back here again. I will remember this moment for the rest of my life.”
Gauff is scheduled to compete again next week in the singles main draw of the BGL BNP Paribas Luxembourg Open in Luxembourg.