Emma Raducanu beat four-time Grand Slam champion Naomi Osaka 6-4, 6-2 in their first career meeting to reach the quarter-finals of the Washington Open on Thursday.
Raducanu, U.S. Open champion in 2021, next faces former world number three Maria Sakkari after the Greek stunned American second seed Emma Navarro in straight sets.
"I thought it was going to be a really difficult match. Naomi's won four slams, she's been world number one, won Masters," Raducanu told Sky Sports. "She's so dangerous and on the hard courts, I think she's particularly comfortable.
"I knew I was going to have to play well and manage my own service games, which I'm really proud of how I did. I was making some inroads in her service game after I got used to it a little bit.
"I'm really pleased with how I handled the ball speed and conditions here in DC."
Raducanu, who will reclaim the British number one ranking from Katie Boulter when the WTA rankings are released on Monday, is also into the women's doubles semi-finals alongside Wimbledon 2022 champion Elena Rybakina.
Venus Williams' comeback tournament after 16 months away from the game ended with a 6-2 6-2 loss to Polish fifth seed Magdalena Frech.
The 45-year-old seven-times singles Grand Slam champion became the oldest player to win a WTA singles match since 2004 when she beat Peyton Stearns in her Washington opener on Tuesday.