Ashleigh Barty has found form ahead of the US Open to claim the biggest scalp of her tennis career, beating seven-time grand slam champion Venus Williams at the Cincinnati Open.
Australian qualifier Barty upset world No.9 Williams 6-3 2-6 6-2 on Wednesday in the second round of the key lead-up event for Flushing Meadows.
It was her first-ever win over a top-10 player.
"It feels really good. To play Venus on such a big stage is a privilege for me and to play as well as I did, I'm really excited," Barty told the WTA website.
"She's a genuine champion of the game and paved the way for us young players coming through.
"It's an honour for me to ... share the court with her, and happy to be moving on."
Barty will face former world No.1 Caroline Wozniacki for a place in the quarter-finals after the sixth-seeded Dane beat Russia's Elena Vesnina 6-2 6-4.
Ninth-seeded Williams, the runner-up at the Australian Open and Wimbledon this year, fell behind Barty 4-1 in the decisive set after dropping serve in the third and fifth games.
The 21-year-old Barty showed plenty of poise and served out to love in the final game to close out the contest in one hour and 50 minutes.
The world No.48 had captured the first set on her fourth set point when she drove a stinging forehand to the back corner of the court that the 37-year-old Williams had no chance to reach.
Williams, in the pair's first ever meeting, rallied in the second set as Barty's serve fell away, but the Australian recovered to win 88 per cent points on her first serve in the decider.
Williams was full of praise for the Australian.
"She just played really well. She found openings in the court, was super consistent, and she just played really well. I just have to give her credit," she said.
Meanwhile, Australian Daria Gavrilova was eliminated by world No.82 Camila Giorgi 7-6 5-7 6-3.
American 16th seed Madison Keys beat Russian Daria Kasatkina to reach the last 16, where she will face fourth-seeded Wimbledon champion Garbine Muguruza of Spain.
Eighth-seeded Russian Svetlana Kuznetsova reached the third round with a win over Kazakhstan's Yulia Putintseva to set up a showdown against Spain's Carla Suarez Navarro.
Germany's Julia Goerges and Slovakian 11th seed Dominika Cibulkova also had wins.