This year’s Wimbledon field has featured a number of notable upsets but none as stunning as the one seen Monday. Top-seeded Ashleigh Barty was defeated by Alison Riske, an unseeded American challenger.

Riske needed three sets to take down Barty, winning 3-6, 6-2, 6-3 to become the first unseeded American to beat the No. 1 seed at Wimbledon since 1994.

The 29-year-old brought dropped the first set and Barty looked strong early on, but Riske bounced back well and found her A-game, especially with her serve. She delivered 12 aces in the victory. She also went four-for-four on break points.

“I haven’t been starting out fantastic in all my matches, but I knew I had the confidence that if I could manage my service games I was going to get looks on her serve,” said Riske, via the AP. “I had to play aggressive. I had to take it to Ash.”

It snaps a 15-match winning streak for Barty, who was playing in her first tournament as the No. 1 ranked competitor on the women’s side. 

Riske will move on to face Serena Williams in the quarterfinals later this week. It’s the first time that Riske has advanced to the quarters of a major tournament.