After the 15-year-old Coco Gauff defeated Venus Williams in her first match at Wimbledon last month, Gauff’s doubles partner, the 17-year-old Caty McNally, had a puncher’s chance at an even bigger upset in her first United States Open. She won the first set against Serena Williams in their second-round match before Williams rallied to prevail, 5-7, 6-3, 6-1.

For only her second U.S. Open singles match she marched onto the court at Arthur Ashe Stadium for the final of the night session with a big grin on her face.

She then made it clear very quickly that Williams, the greatest player of this era, was in for a serious challenge.

Mixing speeds and spins and coming up with big serves when she needed them, McNally applied and absorbed pressure, and converted her only break point of the match to take a 6-5 lead.