Amanda Anisimova ended Naomi Osaka's hopes of back-to-back Australian Open crowns after saving two match points in a night-time thriller at Margaret Court Arena.
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Anisimova rallied for a 4-6 6-3 7-6[10-5] victory in an absorbing two hours, 15 minutes to hand Osaka a first defeat at the Australian Open after winning the first set.
It has now happened twice in a row at Grand Slams for Osaka, who was downed by Leylah Fernandez in a similar fashion last year at the US Open.
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At the same US Open, Anisimova lost a third-set tiebreak to former world No.1 Karolina Pliskova.
Friday's outcome is sure to put that painful defeat a little more into the rear-view mirror.
Anisimova's ranking of 60 is far from representative of her immense quality.
The death of her father in 2019 understandably devastated the 20-year-old, sending her ranking from a high of 21 in 2019 to almost outside the top 90 last term.
She beat Simona Halep at the French Open months earlier – Halep, like Osaka in Melbourne, was the defending champion.
Connecting the dots further, Anisimova would lose to Ash Barty, who happens to be her next foe on Sunday.
Despite the majority of tennis fans looking ahead to a possible encounter between Barty and Osaka when the draw came out, the world No.1 won't be overlooking Anisimova.
She won a second career title at the Melbourne Summer Set two weeks ago and ousted Olympic gold medallist Belinda Bencic even prior to Osaka.
Her 46 winners, including eight on returns, bettered Osaka's 21. Anisimova committed 44 unforced errors to the Japanese star's 45.
"Going into this match I knew I had to be playing sharp if I wanted to give myself a chance," Anisimova said on court.
"Naomi is always going to be playing well. She's an absolute champion, so I knew that I really had to step up my game and try to be aggressive.
"I think that's what I started doing in the second set. Honestly, I am grateful that I was able to play so well today and get this win. It means a lot."
Anisimova thwarted the match points at 4-5 on serve in the third thanks to backhand errors. Anisimova forced one but on the other, Osaka's drive with time found the net. Osaka's backhand had mostly sizzled leading into the Australian Open.
"I thought she played really well," Osaka told reporters.
"For me, I thought it was a pretty high-level match. I think the pace of her ball surprised me, but other than that, it was fun to play."
Osaka took a break from tennis after the US Open but didn't believe a lack of matches cost her, though she said her coach Wim Fissette felt it did.
"He said if I played people that returned as well as she did before maybe I would have been more prepared, but those are the choices that I made," said Osaka.
Anisimova's foothold into the affair came after a first set controlled by Osaka in their first meeting. She cruised in all but one of her service games, while constantly pressuring the Anisimova delivery.
A back-and-forth battle unfolded starting in the second set, Anisimova breaking for 3-1 courtesy of a deft backhand drop shot. A smile followed.
Anisimova's momentum continued in the decider when she grabbed a 15-30 lead on the Osaka serve. But the former world No.1 held, prompting a look of angst from Anisimova toward her high-profile box that included coach Darren Cahill and agent Max Eisenbud.
An Anisimova double fault long – they were serves of intent – contributed to a break point in the next game, though a deadened forehand volley off a venomous Osaka drive saved it.
Osaka saved two more break points for 2-1 as Anisimova was now in the ascendancy, but Osaka pulled ahead 5-4 to ramp up the pressure.
Anisimova survived that 10th game, then set the tone in the tiebreak by claiming the first three points.
An 11th ace sealed matters, before Anisimova dropped her racquet to the court.
"Stepping onto the court, all I'm thinking about is just having fun," said Anisimova.
"Every single day here is an amazing opportunity and experience for me. I'm so grateful to be just playing on this court, so I'm just having fun."