The 18-year-old Mboko, ranked 85th in the world, finished off the 21-year-old Gauff — who had 24 unforced errors — in 1 hour, 22 minutes.
“Your support was incredible,” Mboko told the crowd in French after a chorus of “Olé, Olé, Olé!” chants echoed around the venue. “I’m really happy to win today. .. It’s incredible. I’m so happy to beat such a great champion.”
Mboko will face the winner of the late match between Lin Zhu of China and Jessica Bouzas Maneiro of Spain.
In Rome in May, Gauff rallied to beat Mboko 3-6, 6-2, 6-1.
Earlier, 24th-seeded Marta Kostyuk of Ukraine and ninth-seeded Elena Rybakina of Kazakhstan set up a quarterfinal match. Kostyuk beat McCartney Kessler of the United States 5-7, 6-3, 6-3, and Rybakina topped Dayana Yastremska of Ukraine 5-7, 6-2, 7-5.
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AP tennis: https://apnews.com/hub/tennis