Dart wins the first point of the tie-break, then the second, and then she think she's got the third but it's ruled out.

As she did just a few minutes ago, she unsuccessfully challenges it but still has the mini-break.

An hour has passed and we're still on with this first set.

Quick reactions from Dart earn her the opening point on Tomljanovic's serve and the Emirates Arena reacts loudly.

Tomljanovic takes two points back though, the second an ace, but Dart fights back to level and lets out a huge "COME ON". She's pumped!

The Brit think she's earned a break point but her cross-court forehand is judged out - she challenges it, but Hawk-Eye backs up the original decision.

Tomljanovic goes on to hold and we're headed for a tie-break.

Image source, Getty Images

Mel South
Former British player on BBC TV

The discussion with Anne Keothavong at the changeover will be about ensuring Dart is still doing the right thing.

Tomljanovic has raised her level and it will just be a couple of points that will make the difference in this set.

Dart just needs to keep getting her feet to the ball.

A hold to 30 for Harriet Dart but that was no easy ride for the Brit.

As a Tomljanovic strike sails out to secure the hold, Dart turns to the crowd and tries to whip them up, she wants more noise behind her!

Tomljanovic to serve to stay in the set again.

Image source, Getty Images

Mel South
Former British player on BBC TV

The quality of the hitting from Tomljanovic drew errors from Dart.

Dart was able to dominate on backhand side in the first few games but it's become much more robust on that side from Tomljanovic.

Plenty of balls are coming back now from the Australian. She is showing off what kind of player she is.

And we are level.

Tomljanovic looked to be wrapping up the service game at 40-15 but allowed Dart back in to it, a double fault levelling the score at deuce.

The Australian gets the first advantage but Dart again saves game point, and the Brit then earns a break and set point. Can she make it count? Not this time, firing a forehand into the net.

Dart then puts too much depth on a return and it's advantage Tomljanovic this time. She holds as Dart finds the net.

A fine comeback from Tomljanovic having found herself 0-3 down.

Mel South
Former British player on BBC TV

Tomljanovic stayed patient and took her opportunity when it came along.

She was really shocked with the way Dart came out of the blocks and had to weather the storm, finding a way to make the rallies longer and keep the ball in court.

She gets it! Ajla Tomljanovic gets a breakthrough as Harriet Dart plants a backhand between the tramlines.

The Australian still has work to do though, and will serve to stay in the set.

Image source, Getty Images

Well, well, well, Ajla Tomljanovic has a break point...

Mel South
Former British player on BBC TV

So far Dart's stats on serve have been very impressive.

Points behind first serve 70%, points behind the second serve 62%.

It's whether she can keep the calm and focused attitude in this service game to close out the second set.

Good serving from Ajla Tomljanovic secures her a hold to 30 and so Harriet Dart will now serve for the first set.

In her two previous meetings with Dart, Tomljanovic has lost the first set but come back in three to win.

Mel South
Former British player on BBC TV

This really is incredible. Everything Britain have achieved this week has given them added belief.

A tougher battle ensues on Harriet Dart's serve and the Brit levels at 30-all with a lovely drop shot.

She brings up 40-30 with an even better backhand down the line and finishes off the hold as Tomljanovic is unable to return a serve in.

Tomljanovic to serve to stay in the set.

Image source, Getty Images

A hold to 15 for Ajla Tomljanovic, greeted with a little fist pump from the Australian.

Can she get the break back?

Mel South
Former British player on BBC TV

Dart is not letting Tomljanovic settle and that's what she needs to do.

She can't let her foot off the gas and can't allow Tomljanovic to dictate play which she likes to do.

Dart has hit five winners and Tomljanovic just one.

Dart is on the front foot and being aggressive.

Tomljanovic has to try and absorb this and hope it's just a purple patch.

Ajla Tomljanovic is showing signs of frustration, and it's no wonder. She doesn't know how to handle Harriet Dart at the moment.

She kept herself well in Dart's service game though, levelling at deuce and then saving two further game points.

Dart eventually gets the hold, but are there signs that Tomljanovic is starting to find her feet?

Jonathan Jurejko
BBC Sport

What a transformation we've seen from Harriet Dart this year.

The 26-year-old from London broke into the world's top 100 for the first time in March after reaching the Indian Wells fourth round as a qualifier - and has gone from strength to strength since.

After beating 12th-ranked Elina Svitolina in the Californian desert, she created an even bigger shock by beating world number nine Daria Kasatkina in the US Open first round.

Then, on Thursday, she out-powered and out-fought Spanish former world number two Paula Badosa in one of the best performances of her career.

The hard work has certainly paid off.

Another factor, Dart acknowledged earlier this year, was being happier off the court after coming out of a toxic relationship.

"It's like any job - if you bring things from home into the workplace, it's very challenging," she said.

"I'm a lot happier now."

Image source, Getty Images

Harriet Dart's big-hitting is a sight to behold today. She finds herself 40-15 down but fights back to deuce.

She flips a forehand into the net to gift Tomljanovic the advantage but saves the game point, but the Australian eventually gets the hold and a game on the board.

Mel South
Former British player on BBC TV

It is a fantastic start from Dart.

It was a different dynamic for her coming out here today.

She would have felt disappointment for Heather and it's a different scenario from saying how she had been inspired by Heather's win against Spain.

But she has so much self-belief now she can pull out these big results.