Oh Jo! Konta racks up another break point as she takes Wozniacki to deuce, but lets the Dane off the hook. Wozzy rattles off three points on the bounce to hold. Turning point? We'll see...

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That break does not seem to have helped shift Jo Konta's nerves. A double fault - her first of the match - brings Wozniacki level at 15-15, then she plants a routine forehand into the net at 40-15.

But the Briton regains her composure to see out an important hold.

All sorted. Caroline Wozniacki pulls her grey sock back over her right foot, squeezing into her bright yellow trainer.

Back to business. Konta to serve...

Caroline Wozniacki has a problem. She's calls a medical timeout at the changeover to get some attention for her right ankle. Trainer off, sock off, strapping applied. There is even time for a laugh with the doctor. Maybe she's a stand-up comedian in her spare time.

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Hurrah! A hold, and a comfortable one at that. 

Caroline Wozniacki produces her best service game of the match at a crucial time for her, thundering down her first ace on the way to a hold to love.

Joel Newnham: When Konta gets a chance to come into the net it really works for her.

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And as if we needed further confirmation that nerves were playing a big part, here's some more. Another shaky service game, this time from Konta, is the seventh break of serve in the match. Extraordinary.

Russell Fuller
BBC tennis correspondent

It is not surprising there are so many nerves on display with so much at stake.

Wozniacki will move to the top of the 2017 rankings race with a win: Konta up into second.

Those two consecutive double faults in the ninth game of the first set cost Wozniacki dear and Konta is deservedly shading things for now.

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Just like the first set, Johanna Konta snaffles an early advantage. But it wasn't as easy as you might think. Caroline Wozniacki saves three break points to force deuce, then bats off a fourth. But Konta continues to hammer at the door, forcing it open when Wozniacki's resistance finally crumbles.

Jo Konta has a word with her coach Wim Fissette at the end of the first set. Whatever he said has worked... Konta races into a 0-40 lead in Wozniacki's opening service game.

*denotes next server

Will Carroll: Go Konta! Wow...Odds on a Murray/Konta double at Wimbledon? GB cleansweep? 

Ian Robbins: Good start for Jo but this is still looking like it could be tight.

She can! Phew. 

It is not a smooth-sailing hold for Jo Konta, who has to brush off two break points before clinching the first set.

A wonderful first serve at 15-40 sets the platform, Woznaicki scrambling a return and Konta clubbing a forehand to safety.

She goes out wide again to force deuce, then completes the job to take the first set in 45 minutes.

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Let's see if Johanna Konta can keep her nerve...

Meltdown alert.

Caroline Wozniacki loses her cool at the worst possible time, coughing up successive double faults. She might well have handed over the break points with a bow. An absolute gift.

Johanna Konta snaffles the chance at the first chance - now she will serve for the opening set.

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Tight and tense from both players. Little wonder with the prize at stake.

Back on serve...

Caroline Wozniacki is clearly using that bust-up with umpire Kader Nouni to her advantage. Eyes narrow, glare icy. That's the look towards Nouni after she wins the first point on Johanna Konta's serve. If looks could kill...

Konta tightens up a little, allowing Wozniacki to force deuce.

One, two, three break points are fought off. But not the fourth. She overcooks a baseline return and grimaces.

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Russell Fuller
BBC tennis corresponden

Konta started where she left off in Melbourne. The power that was so apparent in her crushing victory there helped her off to a flyer but Wozniacki has shown how she can stay competitive by varying her spin and taking some pace off the ball.

Caroline Wozniacki stays in touch - spurred on by a bit of a ding-dong with umpire Kader Nouni. At 40-15, the Dane reckons she is put off by a late call from a line-judge, telling Nouni that was the case. He's having none of it. She responds by slamming down a howitzer of a serve, then gives the daggers to the umpire on her way past.

Are we going to see a hold? Yes! Just when Johanna Konta needed it.

There is a sticky moment for the Briton when Wozniacki sticks a lob over her head, moving into the net to volley in a winner for 30-30. 

But Konta responds with a 110mph ace down the T. And then she hammers down another first serve which Wozzy meekly bats back, allowing Konta to despatch with the power of a piston.

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Caroline Wozniacki will be furious with herself. She gained momentum from breaking Konta's service in the previous game - then hands it straight back.

More breaks here than there is at your local A&E department.