Giant-killing Wang Qiang has turned from conqueror to ally for Ashleigh Barty after sending 23-time grand slam champion Serena Williams crashing out in the third round of the Australian Open.
The No.27 seed from China held her nerve in a tense third set to oust the seven-times champion 6-4 6-7 (2-7) 7-5.
The shock defeat means Williams, 38, remains one title behind Margaret Court on the all-time list of women's major winners.
It was Williams' earliest exit at Melbourne Park in 14 years.
Earlier in the day, Barty - who had lost to Wang in the fourth round at the 2019 US Open - outclassed Kazakh Elena Rybakina 6-3 6-2 to set up a fourth-round clash with American 18th seed Alison Riske.
Had they both kept winning, Barty would have met Williams in the semis as she bids to become the first Australian woman in 42 years to win her home grand slam.
Wang was on the verge of what would have been a straight-sets victory when she served for the match at 5-4 in the second set, only for Williams to secure her only break on Friday.
The seven-times Melbourne Park champion went on to dominate the tiebreaker.
But Wang hung tough in a tense final set, securing the crucial break in the 12th and final game with her third match point.
"When you play against her she's a really aggressive player and you can't only be passive," said Wang, whose previous coach was late Australian Peter McNamara.
"You have to stay with her.
"I just tried to be more aggressive - not more aggressive than her, but just try to be my own aggressive way.
"For me this was a really aggressive match.
"She makes more winners than me, but that's the way she plays.
"But I I think she missed a lot today and that's the point."
It was a remarkable turnaround in fortunes in the space of less than five months for Wang, who had won only one game in her previous encounter with Williams in the quarter-finals at last year's US Open.
"After that match I did really hard work in the gym," said Wang.
"I think I have more power than last year."
Wang said she had no plans to celebrate Chinese New Year on Saturday, preferring instead to rest up and prepare for her fourth-round encounter with Ons Jabeur.
The Tunisian sent former world No.1 and 2018 Open champion Caroline Wozniacki into retirement by beating the Dane 7-5 3-6 7-5.
In other thrid-round matches, seventh seed Petra Kvitova from the Czech Republic belted No.25 seed Ekaterina Alexandrova from Russia 6-1 6-2 and Greek No.22 seed Maria Sakkari upset 10th-seeded American Madison Keys 6-4 6-4.
Riske beat Barty's doubles partner Julia Goerges from Germany 1-6 7-6 (7-4) 6-2.
Australian Associated Press