Naomi Broady
British number three on BBC Radio 5 live sports extra at Flushing Meadows

Jo started playing so well, but the errors started to creep up in the second set and the first service percentage dropped. That last service game was a repeat of the second set. Fair play to Krunic, you would not watch this match and think she is ranked 78th in the world, she is playing like a top 20 player.

Konta misses an inviting return at 30-30 in the second game, illustrating her lack of confidence at the moment. She does fight back to force deuce before Krunic composes herself to get her side of the scoreboard ticking.

But it goes from bad to even worse in the Brit's next service game...

Konta somehow plants a volley into the net from close range to gift a break point. The crowd gasp. And then they gasp again when Konta double faults on break point.

Naomi Broady
British number three on BBC Radio 5 live sports extra at Flushing Meadows

Unless you damage the courts or injure people I actually think we should be allowed to smash our rackets and not be fined. It is entertaining.

Right then... Konta to kick off this decider. It's not pretty, it's not particularly effective, but the Briton gets over the line after being taken to deuce by the Serb.

Uh oh, Krunic has a hissy fit after an unforced backhand error hands over the game, bouncing her racquet off the blue acrylic as she shouts at herself. Something Konta can take heart from?

Naomi Broady
British number three on BBC Radio 5 live sports extra at Flushing Meadows

Krunic has the momentum, this could be an important game for the outcome of the match. Krunis is being more aggressive, running balls down, but now she is hurting Jo more, making more winners.

Image source, Rex Features

David Ferrer is indeed out, losing 4-6 6-3 6-2 6-1 to Mikhail Kukushkin on court seven. Over on Arthur Ashe Stadium, Marin Cilic has dropped the third set to Tennys Sandgren but still leads 2-1. Big John Isner is also two sets to one up against France's Pierre-Hugues Herbert, while Jo-Wilfried Tsonga leads Romania's Marius Copil 6-3 6-4 4-3.

Image source, Reuters

Naomi Broady
British number three on BBC Radio 5 live sports extra at Flushing Meadows

I feel like Jo has let this game go, like she wants to just start the third set.

The Serbs are known for being mentally tough. Krunic team looks as equally relaxed as she is, laughing and joking as she wins the set.

Image source, Rex Features

Superb stuff. From Aleksandra Krunic that is, not Johanna Konta. The world number 78 rattles off another hold to love as Konta's returning game also seems to have deserted her.

My prediction of that mammoth hold for 3-3 being the trigger for a straight-set win now looks pretty daft.

But, undeterred, I'll make another one... we will see a different Konta in this deciding set.

What we do know about the 2017 version of Konta is that she will just wipe these past 35 minutes or so out of her mind and start again. Or so we hope.

And still it continues... Jo Konta's service game has gone AWOL. Someone call a search party. It allows Krunic to earn two more break points - she needs just one. A cracking forehand winner leaves her serving for the second set...

Image source, Rex Features

Piers Newbery
BBC Sport at Flushing Meadows

It's hard going for Konta this afternoon, largely down to the fact that her usually excellent serve is misfiring. A paltry 37% of first serves landing in is allowing Krunic into far too many points.

Meanwhile, a ball boy hurls a yellow fuzzy orb over its intended target and into the crowd, endangering the nearby Jeremy Bates. There's drama everywhere you look.

Wow. Aleksandra Krunic expended a lot of energy in that previous game, but you wouldn't know it with the speed she rattles off a hold to love. Konta doesn't return a clean ball in a game which lasts barely a minute.

Naomi Broady
British number three on BBC Radio 5 live sports extra at Flushing Meadows

It shows how hard Jo hits the ball, that she has a player down the other end, who is one of the most consistent and fastest players on tour and she can't get that return back.

Image source, AFP

Another break point comes and goes for the Serb before Konta finally finds her first serve - they've been in short supply - to take control. The seventh seed almost bruises the ball with a blistering forehand winner which leaves Krunic wafting at thin air and then wraps up a gutsy hold with a service winner.

That, I'd suggest, is a big hold. And probably, maybe, the difference between a straight-set and three-set win.

Two more break points for Aleksandra Krunic.

One disappears when Konta outpowers her in a baseline rally, battering away a backhand winner, then volleying some verbals at her box. Konta channels any lingering anger by hammering down an ace to wipe out the second break point.

Krunic rushes into a backhand from the baseline when she doesn't need to, almost hitting the net post, but then responds with a clever shot that takes the pace off Konta's pass and leaves the Brit unable to clip a cross-shot at the net to safety.

More heavy footwork from Konta brings up a third break point for Krunic... second serve... and a brilliant pickup - under pressure - saves it.

Back to deuce...

Elsewhere, 21st seed David Ferrer is in trouble - big trouble - trailing world number 103 Mikhail Kukushkin by two sets to love and 5-1 in the fourth set. The end appears to be nigh for the 35-year-old.

Image source, Getty Images

Johanna Konta is still not finding her best rhythm. Nevertheless it is enough to hold as Krunic cannot ask any questions of her serve.

The Serb, who reached the fourth round here at Flushing Meadows in 2014, crashes out an easy hold to love in the next game, Konta looking pensive as she trudges back to her chair.

Image source, AFP

Just don't open the voddy before a match, eh Naomi...

Naomi Broady
British number three on BBC Radio 5 live sports extra at Flushing Meadows

The US Open is one of my favourite Grand Slams, it might have something to do with staying in Manhattan. I also love food and there are so many restaurants in Manhattan.

This year is sponsored by a department store and we went into a gifting room and were told we could take one of everything. I took headphones, a posh scented candle - who doesn't love a scented candle and a bottle of vodka.

John McEnerney: Muguruza or Pliskova are the form players but the US Open sometimes throws a surprise winner maybe it's Wozniacki's time to win her first.

Image source, Getty Images

Another chance blown for Konta. The British number one was ruthless in the opening set, converting all three of her break points. Now she has allowed Krunic to wriggle off the hook again. The Serb digs deep to hold again.