Bianca Andreescu staged a dramatic comeback on Sunday to topple Garbine Muguruza in a battle of former Grand Slam champions on day one of the Adelaide International.
The Canadian, who won the 2019 US Open, was crushed in the first set and slipped 2-5 behind in the second before surging home 0-6, 7-6 (7/3), 6-1 to get her 2023 season off to a winning start.
It maintained her perfect record against two-time Grand Slam winner and former world No 1 Muguruza, improving to 3-0.
"In the second set I really had to change my game plan," said the 22-year-old, who has slipped to 46 in the world.
"I told myself to go for it, whatever happens, happens. I put more returns in the court, more serves in the court. I'm so glad I pulled that out, I have no idea how."
Spain's Muguruza, who won the French Open in 2016 and Wimbledon a year later, claimed the first set in commanding fashion, outnumbering Andreescu in winners eight to two, not facing a break point.
Andreescu started the second set more strongly, only for Muguruza to break for 4-2 and then consolidate for 5-2 with serve.
But she couldn't close out the victory and Andreescu took it to a tie-break where a sizzling backhand winner gave her pivotal 4-2 lead.
A demoralised Muguruza had no answers as the Canadian swept her aside in the third set to set up a second-round clash against either fourth seed Veronika Kudermetova or Amanda Anisimova.
In other singles action, Estonian veteran Kaia Kanepi also came from behind to outlast Belarusian Aliaksandra Sasnovich 4-6, 6-1, 6-4 and will next meet either Ekaterina Alexandrova or Marketa Vondrousova.
Americans Shelby Rogers and Claire Liu also progressed.
Top-ranked Novak Djokovic headlines the men's field and is set to play France's Constant Lestienne on Monday in his first match in Australia since being deported last year over his Covid-19 vaccination stance.