What a shot! And what a time to bring it out. Konta is aggressive and bold in search of another break and when she gets it she doesn't disappoint. 

Petkovic stretches at her cross-court forehand in desperation. Big point from the Briton. She's serving for the set.

Both players are feeling the pace now. Petkovic just manages to return on the stretch and Konta summons the composure to level at 15-15, right in the corner.

Another shot from Konta into the net for 30-30 - she looked sluggish there, but so does Petkovic, too. Her return slumps into the net,  a chance for a third break for Konta. 

It's a question of who can last this rally longest, Konta goes for the killer shot, a sweeping forehand, but it's just wide. Level at deuce.

This is brilliant in reply, from Konta. She knows she has to win this game and goes after it bravely, Petkovic can only hold on but Konta raises the pace to storm into a three-point lead. 

With the game in sight Petkovic raises her resistance, Konta can still finish things with a simply forehand, but it's too long. And again on the next point. 

Is Petkovic back in? Deep breath from Konta, and a scream of delight as her opponent hits long. 

More searing aggression from Petkovic. She's really in the groove, zooming into a three-point lead. Great mobility - Konta's looking very static by contrast. That's seven points in a row. 

Can she make it eight? Konta stubbornly rallies but Petkovic saves the best until last, a searching two-hander to the back corner for the game. 

Image source, AFP

Petkovic really is rattled. She's been given a warning for having a dispute with her racquet.

Is she good when she's angry? She hits back with two deep returns, the forehand looks good here. Konta then double faults and Petkovic sees out the game with ominous ease. Cue fist pump.

Piers Newbery
BBC Sport at Flushing Meadows

"It's 22C with a cooling breeze on Louis Armstrong this morning, the best conditions of the week for players and spectators. Konta continues to look calm and determined, as she has in winning four matches already in New York, and the Petkovic forehand is starting to break down."

Image source, Reuters

So close. All the groundwork had been done. With Petkovic on the back foot Konta falls short with a drop shot at the net, wide.  

How to respond? With a rasping forehand Petkovic can only wave at. Then a tremendous backhand to the far corner for 30-30. Petkovic is rattled, she shoots wide and it's break point. Petkovic defends it - thanks to a lucky bounce off the net - but then shoots wide again. Konta has her on the rack, Petkovic goes for an ambitious diagonal passing shot, and once more it's wide. Konta breaks!

Petkovic thinks Konta's broken but she is calm. She powers through this one with her opponent hounding her at the net. Great poise to hold her serve. 

Image source, Reuters

Konta goes straight onto the front foot again, some excellent net play. There is some flair and flourish but it's all within her rhythm. Petkovic meanwhile, has got a change in pace in her and Konta's two-point lead is gone in no time.

It's break point as Konta's laboured forehand hits the net, but Petkovic hits long for deuce. Now is the time to raise your game and Konta obliges and goes on the attack. Petkovic is no slouch though and hits back straight away to level again. 

Wonderful stuff from Petkovic. Aggression, technique, poise. She's got it all as she powers into a volley for a two-points cushion. Konta can't keep up with this, she hits the deciding return wide. Petkovic sails away with this one. 

Ace. The first of the match. Is Konta in the groove? It's all very methodical, very composed, but it's just lacking that killer aggression. 

Now she goes on the attack though, racing to the net and Petkovic goes long, too long. One point to wrap it up and she finds it. Petkovic returns to the net. 

Image source, Getty Images

This is better now as Konta shows a bit of hustle to win the first two points, but Petkovic is not ruffled. She goes on the attack big time, powering up to the net and delivering a sumptuous drop shot before dropping back for a massive forehand on her next. 

Level at 30-30, where is it headed? Konta comes back for her first break point, Petkovic fluffs her first serve and takes an absolute age for the second before hitting one long. Game on.

Double fault for Konta on her first serve and the nerves don't stop there, she drags a simple looking forehand way, way wide.

Petkovic can smell a break and she turns on the power for a passing winner for 0-40. Konta recovers for 30-40 but the German is too strong. Not the start Konta had intended.

Piers Newbery
BBC Sport at Flushing Meadows

Judy Murray knows Konta well through her role as Fed Cup captain, and told BBC Radio 5 live how a demoralising defeat in February pushed Konta to working with a sports psychologist: 

"On the last day we played Belarus to get out of the group and she had a bit of a horror. She suffered from really bad performance anxiety. 

She lost that match very quickly and was distraught afterwards. It was really a question of her recognising she needed to do something to help her control her emotions and her mind."

Murray believes Konta has "a real good shot against Petkovic", adding: "You go after that forehand side big time. 

"That was exactly what Jo did to Muguruza. If she plays in the same way and is able to stay as calm and composed as she was in the last match, I can't see any reason why she can't get through another match."

A bit of a rusty start from Petkovic as she hits two shots into the net, Konta can't take advantage though and the German soon levels at 30-30, Konta hitting long. 

Petkovic then gets lucky with what looked like a dud of a forehand reply, it hits the top of the net, bounces out of reach, Konta can't make it and Petkovic eventually sees the game out with a strong serve, having briefly been pegged back to deuce.

Here we go then, play is under way

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Image source, Getty Images

Now then, with the players out on court already, warming up, I don't think we've got time to delve too deep into this one. 

But it does remind me of a story I was told. A friend was seeing a German girl, who eventually ended things by explaining: "I need to see the skeleton of my chaos."

As brush-offs go, I'm yet to hear a better one.

Piers Newbery
BBC Sport at Flushing Meadows

Image source, Getty Images

"Andrea Petkovic is generally regarded as about the best interview in tennis, with a razor-sharp wit and interests ranging from philosophy, to literature, to an absolute love of music. 

"Whether it be The National, Arcade Fire or The Smiths, the Bosnia-born German is an indie kid at heart. After several serious injuries, she has also become a world class player over the last two years, with a Grand Slam semi-final to her name in Paris last year."

Good afternoon and welcome.

In case you didn't know, the other reason why Konta's win was such a big deal is because Muguruza is ranked eighth in the world. Konta is the world number 97 right now.

Her opponent today, German Andre Petkovic, is ranked 18th. 

So even if she does make it through to the fourth round, there's an argument to suggest the Muguruza win could still be her best ever (or so far). But not just because of the rankings.

The manner of that victory - grueling, determined, resilient - suggests the makings of a mentality that could carry Konta, 24, much further still.

Until now, the consensus seemed to be that there was potential, but something still was lacking. 

Will we be saying the same in a few hours' time?