Great depth from Zheng keeps Kalinskaya pinned to the back of the court as the Chinese 12th seed takes charge on serve.

She's served the most aces in the women’s singles draw this year and adds another to her tally for 40-0, but a couple of misses suddenly give Kalinskaya a chance.

Another error. From nowhere, an opportunity arises for Kalinskaya.

Zheng is ready at the net to volley in and reach deuce on Kalinskaya's serve, but the Russian rises to the challenge once again to hold.

It's heating up nicely, but can Zheng force the breakthrough she needs?

Image source, EPA

Brit Neal Skupski and American partner Desirae Krawczyk, who earlier reached the mixed doubles final with a 6-4 6-1 victory over Australian wildcards Olivia Gadecki and Marc Polmans, now know who they'll face in the final.

The British-American second seeds will face third seeds Su-Wei Hsieh of Chinese Taipei and Pole Jan Zielinski. Hsieh and Zielinski prevailed 7-6 (10-8) 6-2 on Kia Arena against Jaimee Fourlis and Andrew Harris, who were also Australian wildcards.

Both players are locked in now and there's much more quality on show at the start of this second set.

Zheng wins an important fifth point with a forehand for 40-30 before a first serve helps her settle this latest game.

Anna Kalinskaya is made to come through a thorough examination in her first service game of set two, but she does so in style after chasing down everything Zheng can throw at her before unleashing a backhand down the line to hold after the 12th seed had followed her to deuce. Very well played.

Image source, Getty Images

Briton Andy Lapthorne was knocked out of the quad wheelchair singles but won in the opening round of the doubles competition.

Sixteen-time major winner Lapthorne, 33, lost out to second seed Sam Schroder 6-1 6-0 in the singles quarter-finals.

But Lapthorne returned to action alongside American teammate David Wagner to win 6-0 6-1 in the doubles quarter-finals against Turkey's Ali Ataman and Brazil's Ymanitu Silva.

The British-American pairing will face second seeds Heath Davidson of Australia and Canadian Robert Shaw in the semi-finals.

Davidson and Shaw knocked out Brit Gregory Slade and Australian Finn Broadbent 6-0 6-0 on Kia Arena. Slade was a wildcard in the singles competition but lost to Chile's Francisco Cayulef in the first round on Tuesday.

Work for Zheng Qinwen to do after losing an hour-long first set in a tie-break, but it feels like this is there for the taking for either player if someone can maintain a consistent level.

Lots of ups, downs, twists and turns so far. And that was just the tie-break.

Zheng begins her response with a love hold.

Image source, Getty Images

Neal Skupski and Desirae Krawczyk have a chance to win their third mixed doubles Grand Slam title together after beating Australians Olivia Gadecki and Marc Polmans in the semi-final.

"It would be nice to add to the collection, but it is one point at a time," said Britain's Skupski. "It's the first time in the final in Australia and Desirae is going for all four Grand Slams in her career."

Krawczyk added: "It was a tough match but we got a couple of points over them and we just tried to stay in the moment, do the small things, do what we do best and try to not get ahead of ourselves."

They will play the third-seeded pair of Taiwanese player Hsieh Su-Wei and Poland's Jan Zielinski after they defeated Australian duo Jaimee Fourlis and Andrew Harris.

Krawczyk and Harris are in a relationship and Krawczyk expected them to be on opposite sides of the court in Friday's final.

"I thought I was going to be playing my boyfriend. Tough loss," said Krawczyk.

Skupski added: "It's going to be very difficult. Zielinski likes playing in Australia and Hsieh is a legend of the game and she seems to just be getting better. She is very talented so we will have to do our homework."

Impressively done!

Russia's Anna Kalinskaya, who had never gone beyond the second round at a Grand Slam before this year's Australian open, drives in a backhand to take the opening set against 12th seed Zheng Qinwen to move one set away from a place in the semi-finals.

Big miss on a very big point by Zheng!

Kalinskaya has two set points.

The misses continue to come in this high-stakes first set tie-break.

We're back on serve with the 75th-ranked Kalinskaya 5-4 up and within touching distance of the set.

Another miss from Kalinskaya gives Zheng the mini break but the Russian responds with an excellent forehand winner to level at 3-3.

It's impossible to tell which way this is going...

Kalinskaya doesn't get off to an ideal start in the tie-break as she misses with a forehand, but Zheng falters on the next point before firing in an ace to bring us back on serve.

Zheng produces a couple of huge serves to set up the tie-break.

Here we go!

Are we destined for a tie-break?

It's looking that way as Zheng Qinwen slams a spectacular backhand down the line for 30-0.

Kalinskaya produces a timely first serve to draw level at 30-30 before targeting Zheng's forehand to win a couple of cheap points and efficiently close out a game which had threatened to prove a tricky one.

The Russian is one break of serve away from the set again.

A brilliant backhand from Kalinskaya wrong-foots Zheng for 15-15 but the 21-year-old fires back with a powerful forehand and a clever, disguised drop shot catches the Russian out for 40-30.

A whipped forehand finds the line and Zheng punches the air as she completes the hold to stay in contention in the first set.

Anna Kalinskaya responds with a comfortable hold of her own to edge back in front, and potentially one game away from the opening set.

The Russian puts away an ace for 40-0 before sealing the game a couple of points later.

The pressure is all on 12th seed Zheng Qinwen now.

Jonathan Jurejko
BBC Sport in Melbourne

The carousal nature of professional tennis - whether it is players ditching coaches, vice versa, or doubles partners breaking up the partnership - can often lead to drama.

Zheng Qinwen has been right in the thick of it recently.

First, her partnership with coach Pere Riba - who guided her in 2022 when she cracked the top 30 and won a first WTA title - ended after Roland Garros last year.

Zheng started working with Naomi Osaka's old coach Wim Fissette. Riba linked up with Coco Gauff and helped her win the US Open title.

Got it? Stick with me.

Shortly after Flushing Meadows, Fissette ditched Zheng - who was fuming about the decision - to work again with the returning Osaka.

Riba, meanwhile, left Gauff's team just before the WTA Finals. Now he's back working with Zheng as she aims to reach a first major semi-final.

"I'm happy to be here, to have my team back," says Zheng.

"There is nothing I want to say about Wim Fissette."

A rare, uncomplicated hold to love for China's Zheng Qinwen - the first in a quarter-final match which has already seen four breaks of serve.