Katie Boulter stunned world number five Jessica Pegula for the biggest win of her career to give Great Britain a 1-0 lead over the United States at the United Cup in Perth.
It marks the 27-year-old's first victory over a top-five opponent.
If her team-mate Cameron Norrie beats Taylor Fritz, GB will qualify for the quarter-finals of the tournament.
In January 2023, the first edition of the mixed-team competition, Pegula led the US to the United Cup title, but on Sunday she was forced to save three Boulter set points at 4-5 in the opening set.