In case you weren’t up late Saturday night watching tennis, you may have missed one of the great upsets of the 2014 Sony Open Tennis tournament thus far. American Coco Vandeweghe, who entered the main draw as a qualifier, upset former U.S. Open champion Sam Stosur on Stadium Court, 5-7, 7-5, 7-5 in a match that ended at 2:29 a.m.

For Vandeweghe, the athleticism comes naturally. Her mother, Tauna, was a U.S. Olympian in swimming in 1976 and volleyball in 1984, and her uncle is former NBA star Kiki Vandeweghe. The 22-year-old will face world No. 1 and Sony Open top seed Serena Williams in Monday’s Day Session in a fourth-round match.

All Vandeweghe has done so far is upset two seeded players on her way to Serena, who she faced in her first WTA final in 2012.