MELBOURNE, Australia - The unseeded Anastasia Pavlyuchenkova delivered a performance of irresistible quality to come from a set and a break down to upset No.5 seed Sloane Stephens 6-7(3), 6-3, 6-3 over two hours and 32 minutes at the Australian Open.

The Russian continued her stellar streak at this stage of a major: she has won her last four, once at each Slam, out of the five times she has progressed to the round of 16. Today's result marks the first time she has notched up a second last-eight showing at any of the Grand Slams, having previously made the Australian Open quarterfinals in 2017.

Pavlyuchenkova, whose career high ranking is World No.13, has built a reputation as a giant-killer over the course of her career, and her victory today marks her 30th Top 10 win and 13th over a Top 5 player. However, it is just the second of the latter that has come on the Grand Slam stage, following her triumph over compatriot Vera Zvonareva at Roland Garros 2011.

2013 semifinalist Stephens had snapped a five-match losing streak in Flinders Park stretching back to 2014 this year, and had looked increasingly dangerous over the first week. Taking the court at 11.21pm, the 2017 US Open champion was razor-sharp out of the blocks, winning two key mini-battles - a four-deuce return game, converted on her fourth break point with a backhand winner, and a subsequent hold from 0-40 - to leap to a 3-0 lead.

Pavlyuchenkova, meanwhile, was beset by wild groundstrokes and poorly executed dropshots. But, staring down a 0-40 barrel of three points to fall 1-5 behind, the Russian pulled herself together. Two crosscourt backhand winners, a series of pummeling forehands and a breathtaking stab volley later, Pavlyuchenkova was off and running. A backhand pass sealed the break back in the next game, and the 27-year-old fended off another two break points to pull the score level at 4-4.

Stephens, though, did not let those missed chances faze her, keeping pace with Pavlyuchenkova through a high-quality stretch of play into the tiebreak. There, she took control with a succession of her signature scorching inside-out forehands before Pavlyuchenkova, having battled all the way back into the set, conceded it with a double fault on the first set point against her.

"I went out and I was really sluggish," recalled Pavlyuchenkova, who also described how her energy levels had kept going up and down over the course of the match. "Like, damn, this match is so intense, why am I feeling like I'm going to fall asleep? She started really well, more aggressive than usual, so I was not quite ready. Being 1-4 down and 0-40 and always coming back took a lot of energy out of me - but by the end of the set I started to figure it out."

As in the opening set, it was Stephens who leapt out to the initial lead in the second set. And once again, as Pavlyuchenkova committed an array of wild errors to fall behind 0-2, 0-30 on her serve, one-way traffic seemed imminent. But just as before, the four-time Grand Slam quarterfinalist gathered herself.

Swinging from the hips, Pavlyuchenkova turned her power up to full throttle as she bulldozed through six of the next seven games. Though Stephens' proficiency on the low, dipping backhand pass had served her extremely well to this point, the Strasbourg champion persisted in making her way forwards - and it began to pay dividends as she won eight of 13 points at net, frequently with brilliant reflexes and sharp angles.

Warming down afterwards, Pavlyuchenkova said she had started to use her brain more to work out Stephens' strategy. "Sloane is very creative and she has a lot of strokes - I actually like her game because she can stay passive and move well, or she can be aggressive and hit winners," she said. 

"I was like, I think she's waiting for me to miss. She was giving me short balls and every time I came into the net, bam, passing shot. I was frustrated and it was working. I was like, think now! Slowly I was beginning not to play stupidly aggressive but to create something that she doesn't like."

Towards the close of the second set, the level of play rose to an extraordinary level as Pavlyuchenkova's all-out attack met Stephens' wall-like defence. But even ridiculous shots from the latter such as the full-stretch lob in the eighth game weren't enough to shake Pavlyuchenkova from her mission, and she blitzed a backhand down the line to close out each of the set's final two games.

There was a sense of delirium around Rod Laver Arena as the clock neared 1am and the pair embarked on the deciding set with a 15-minute game that could have functioned as a highlights reel all of its own. Eight times Pavlyuchenkova, throwing everything she could at Stephens, made her way to break point; eight times Stephens repelled her with clutch serving and dogged defence.

Eventually, it was the Miami champion who successfully held on, Stephens cracking a backhand pass to win her second game in seven. But in a match full of twists and turns where no lead ever seemed totally safe, it was Pavlyuchenkova who responded to the loss of that epic game by raising her level. A swift hold levelled the score at 1-1 and put the ball firmly back in Stephens' court again.

Thereafter, the return would be the crucial stroke of the match. There would be only one further hold, by Pavlyuchenkova in the sixth game - but despite the 12-time WTA titlist's radar often going askew behind her own serve, she was laser-focused in punishing her opponent's delivery.

Laying into the Stephens serve relentlessly, Pavlyuchenkova's shotmaking ran rampant as she raised her tally of winners to 46 (against 53 unforced errors). Dropping serve to love in the penultimate game was merely a minor blip: Pavlyuchenkova turned round to power through nine of her final 10 return points, breaking Stephens to 15 and sealing victory at 1.53am with, appropriately enough, a wonderful reflex volley.

Grand Slam quarterfinals are familiar terrain for Pavlyuchenkova is used to: she has been to four in singles and five in doubles. However, with a 0-9 record combined, what lies beyond is been unattainable so far. Next week offers a chance for the former junior World No.1 to break her duck against another unseeded opponent, Danielle Collins.

"I don't know what to expect," said Pavlyuchenkova of her first meeting with the American former college player, who only turned pro in 2017. "I've never played against her and didn't know much about her until last year. Most of the girls were starting to discover her then - who's this girl, she's playing good?"

However, Pavlyuchenkova hopes that she will be able to draw on her previous experience for a different result. "Not being satisfied that I'm in the quarterfinals," she said would be one key difference. "Just to take it as a new match and new challenge. And don't be so nervous about it, just enjoy it. This means a lot but I want more. I've had quarterfinals - I want to go further."