The first challenge of the match goes Watson's way and that helps her battle her way to deuce.

Konta is on the chase throughout the rally but Watson, searching for the big winner, overhits. Konta can't make it count though as she errors on her backhand.

Watson's first serve isn't quite there and the advantage goes back Konta's way. Konta sprawls, trying to meet Watson's return from right on the baseline, but she can't control her shot. Back to deuce we go.

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Can Watson stop Konta before she finds her full rhythm? She takes a deep breath as she readies herself to seve.

A competitive first set but Konta looks to be settling into her rhythm now. That was her first love hold of the match.

Oh, Konta's backhand is full of aggression and Watson teed that up perfectly for her. 

In fact this entire game is full of typical Konta spice, her slice serve completely beating Watson to make it 40-0.

Cross court goes Konta, and that's the winner! She'll take the first set.

A cracking serve from Watson gives her the advantage but she double faults again.

That allows Konta to get a break point and there's a yell from Konta as her backhand goes whizzing across the court, out of Watson's reach. 

She'll serve for the first set.

This is turning into a real tussle, Konta making a few errors as she tries to turn and get the big forehand winner across the court.

She gets lucky with another net call, forcing the game to deuce, but her forehand return is horrible. It takes the top of the racquet and that's advantage Watson.

That is utterly superb from Konta. Ooft. A forehand winner, Konta moving in perfect rhythm to send the ball right down the line and wrongfoot Watson. Back to deuce we go.

Watson finds herself with a 0-30 lead as a backhand volley from Konta goes awry.

In fact this is as messy from Konta as the opening game and Watson speeds to three break points. And Watson's broken straight back! Konta grimaces as her forehand sails into the net. Now then...

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Konta has asked to see her coach, Wim Fissette. "Keep doing really well and keep trusting what you're doing," is his advice. She's a break up and moving much more fluidly around the court.

Watson tries a drop shot but Konta is wise to it. She's so quick on her feet to meet it and pop it back over. She squanders the advantage though as Watson forces an error with her serve.

Both players push each other into the corner of the court but it's Konta who has the better of the second deuce. She makes her second advantage count too, winning a mini-tussle at the net as Watson's dink bounces out.

A hint of frustration in Watson's face as Konta climbs to a 0-30 lead, but a lovely backhand, catching Konta unawares as she darts around behind the baseline, gets Watson on the board.

That's too good from Konta though. With pinpoint accuracy she nails a forehand down the line, Watson unable to do anything but watch the ball sail by her.

Watson saves a break point with an ace and then another good first serve takes it to deuce.

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Konta's range is still a little wonky and she can't quite unfurl that big serve. However Watson's backhand goes skew-whiff and Konta claws it back to 30-30.

It's Watson who is doing most of the running and she can't get to Konta's little dink over the net. A shout of annoyance from Watson as she floats her backhand into the net, and Konta holds.

It's a positively balmy 28 degrees in California at the moment. It's a test of stamina for these two.

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Konta draws Watson up to the net, trying to trick her, but it's Watson who has the better of the point as she runs, reaches and bunts the ball back over.

Konta then decides to go on the move, volleying with plenty of pace to take it to 15-15. She's starting to find her range, moving more freely across the court, and she forces it to deuce with a powerful forehand.

Watson targets Konta's backhand and it works, giving her the advantage. Down comes the serve, and that's a hold for Watson.

Will that help Konta settle down? Watson comes up to the net, trying to dink a backhand over, but she misjudges her line and the ball goes out.

There's plenty of aggression from both players, Watson first clawing her way to a break point with a cross-court winner, before she overhits her forehand to take it to deuce.

Konta then sets herself up perfectly to drill a winner down the line, before an overhead smash ensures she holds her serve. All square.

Konta shuffles forward, trying to get her forehand past Watson, but her opponent is having none of it. Watson stands deep on the baseline and batters a forehand that Konta can only return into the net.

Ooh, that's not great from Watson. She misses three serves in a row, follows it up with a cracking ace, and then misses a run of serves. She looks irritated as Konta breaks straight back - she knows she's gifted her a game with three double-faults.

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And Watson breaks! She's been quick on her feet and she's thrown everything into her forehand. She's certainly the more comfortable of the two at the moment.

This is a really positive start from Watson but Konta is still strong on her serve and she wins her first point with a winner that Watson tamely returns into the net. 

Lovely stuff from Watson in response, winning a long rally as Konta sprawls to meet a forehand. Watson, quick on her feet, darts across and sends a winner cross court.

A lucky bobble off the net from Konta takes it to 40-40 and she soon gets the advantage, but that's excellent from Watson. She's aggressive with her forehand, and it's back to deuce we go.

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Watson beats Konta with a serve before targeting Konta's forehand, forcing her compatriot to over-hit.

In fact Konta's not found her radar quite yet, battering a loose forehand out of bounds, and Watson keeps targeting her forehand. That's a relatively straightforward hold to love for Watson.

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Heather Watson bounces the ball, steadies herself and throws the ball up into the air. Here we go.