Teenager Mika Stojsavljevic stunned Talia Gibson, ranked more than 200 places above her, in straight sets to give Great Britain a 1-0 lead over Australia in the Billie Jean King Cup.
The world number 275, making her debut in the competition, clinched the first set in the tie-break after letting a 3-1 lead slip.
The 17-year-old later saved five break points in the penultimate game of the match before converting her first match point to close out a 7-6 (7-4) 7-5 win over Gibson, 65th in the WTA rankings, in just over two hours in Melbourne.
“It feels amazing. I can’t believe it. I can’t even remember the last point,” Stojsavljevic said. “I had amazing support from the side and managed to get through.
“It was a good match. We have very similar games, both quite aggressive, so I’m happy to get through it.”
Stojsavljevic is the second-lowest ranked player in a Great Britain team missing Emma Raducanu, Sonay Kartal, Katie Boulter and Fran Jones – all of whom are ranked inside the world’s top 100 for singles.
The 2024 US Open junior champion was sitting her GCSE exams when she competed at the WTA event in Nottingham last June before enjoying sustained success in the autumn with a run of three finals, including taking an ITF-level title in Birmingham.
Britain’s Harriet Dart is in action against Kimberly Birrell in Friday’s second singles match, with a doubles and two reverse singles to follow on Saturday.
The winner of the best-of-five tie will advance to the eight-team finals in Shenzhen, China, in September, while the losers face a play-off in November.