MIAMI, FL, USA - No.12 seed Ashleigh Barty maintained her unbeaten record over Kiki Bertens to move into her maiden Miami Open quarterfinal, coming from behind to defeat the No.7 seed 4-6, 6-3, 6-2 in one hour and 53 minutes.

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The Australian now leads the head-to-head against Bertens 4-0 - with three of those wins from a set down, their first encounter in Brisbane qualifying in 2014 and their most recent before today, a 6-7(4), 6-4, 7-5 epic in the Sydney semifinals in January.

Barty sprinted out of the blocks once again in the first match on Butch Buchholz Court. Dictating with her forehand and conjuring up a brilliant pass on the run en route to breaking in the second game, the 22-year-old won 12 of the first 16 points to leap to a 3-0 lead over Bertens, whose backhand in particular was repeatedly finding the net.

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But the St. Petersburg champion roared back with gusto, essaying a 180-degree turnaround to reel off six of the next seven games and snatch the opening set. A commitment to coming forwards was key: Bertens, who has won 10 doubles titles on the WTA Tour, excelled at net, finishing points efficiently with finely judged angles.

Gradually, all the elements of Bertens' game began to fall into place as the 27-year-old ironed out her errors, levelling at 3-3 with two aces in a row. Increasingly unbothered even by Barty's biting slice, Bertens was able to maintain aggressive positions from the baseline - and to respond with even more effective finesse of her own, successfully breaking up the rhythm with perfectly executed dropshots.

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Although Barty struggled to find her range off the ground for much of the second set, ending a number of otherwise riveting all-court points with anticlimactic errors, the Zhuhai Elite Trophy champion did a superb job of raising the efficiency of her serve in order to keep the scoreboard close. "Knowing that I have plans A, B and C that I can go back to, particularly with what serves I like to hit, that's a pretty good step," Barty said with satisfaction afterwards.

The fifth game was crucial: lapsing into impatient mistakes, Barty found herself having to stave off three break points. But the Australian Open quarterfinalist found some magic on each one: a cunning short slice winner, a backhand pass and spectacular reflexes to triumph in a thrilling net exchange.

"Whenever I play Kiki, there's really not much in the match at all," Barty told the press afterwards. "For a span of six or seven games there she maybe gave me one or two errors - she really went into lockdown mode. I did well to squeeze out of my service game at 2-2 in the second, had a little wriggle there and went into lockdown mode myself."

Barty also paid tribute to new performance coach Ben Crowe for helping take her game to a new level following what she admits was a "disappointing" Wimbledon last year, ending in a third-round loss to Daria Kasatkina. "He's made an astronomical difference," she said. "We've created a really tightly knit group: we trust each other, we bounce ideas off each other and ultimately we try to get the best out of each other."

Three games later, it was Barty excelling with the dropshot to give herself a chance to break - and she seized it immediately as Bertens sent a forehand into the net. Pinning the Charleston, Cincinnati and Seoul champion into her backhand corner, Barty served out the set with a minimum of fuss.

The Bertens forehand morphed from weapon into liability as the momentum continued to swing Barty's way in the deciding set. Two errors from that wing paved the way to an immediate break of the Bertens serve; another two saw her fall behind a double break for 0-3.

By contrast, Barty could now do little wrong with her own forehand, and a hold comprised of three unreturnable serves and one ace underlined her confident form.

A minor lapse to concede her own serve in the fourth game was swiftly put behind her as more brilliant shotmaking saw Barty break again for 4-1, and this time the Sydney runner-up would hold on to that lead, closing out on her first match point as a Bertens backhand sailed long. Up next will either be Barty's conqueror in the Sydney final, No.3 seed Petra Kvitova, or No.19 seed Caroline Garcia - and a quarterfinal win over either would secure a Top 10 debut for the World No.11.

"Absolutely not!" Barty responded when asked whether she was tired of facing Kvitova, who also ended her Australian Open run and whom she has never beaten. "It's always an exceptional challenge, she's one of the best in the world - if it is Petra, I look forward to it. She moves well for a girl her size, and when she gets a strike on the ball, no matter what position on the court she's in she can hurt you - so the key will be to get her off balance and out of position."