Those aces are coming up clutch for Coco Gauff. She saves another break point with one.

Nope, says Coco Gauff. A sizzling ace brings us to deuce.

Now then, is there one last surprise in store?

Varvara Gracheva has got herself a break point.

Coco Gauff misses the first break point, but she's gifted another through a Varvara Gracheva double fault.

Oh no! Another double fault. Disaster for the world number 66 as a second set bagel is looking very likely here.

Gauff is just one game away from a very comfortable first-round win.

Jan Choinski is still putting everything into these shots and he overpowers Roberto Carballes Baena with some crushing forehands to open up a 30-15 lead.

The Briton then double faults but isn't phased as a forehand winner down the line and a giant first serve secure the hold.

Carballes Baena to serve for the match...

Lovely stuff from Coco Gauff. The 20-year-old somehow manages to reach a ball at the net before squeezing in a backhand winner.

Varvara Gracheva misses on the next point and it's break point Gauff.

Roberto Carballes Baena opens up a 40-0 lead before Jan Choinski hammers a forehand winner down the line.

It's in vain, however, as the Briton spoons a forehand long and the Carballes Baena is now within one game of victory and reaching the second round of the US Open.

Image source, Getty Images

A big second serve sees Coco Gauff through another close service game.

Defeat for Varvara Gracheva is looking inevitable now. That's seven games in a row she has lost.

Naomi Broady
British player on BBC Radio 5 Sports Extra and BBC Sounds

Jan Choinski raised his level as we saw there and when he does that he is kind of unplayable.

A tired-looking backhand into the net from Jan Choinski sees Roberto Carballes Baena hold to 15.

We're four hours and 15 minutes into this match, which is taking place in temperatures of around 30 degrees Celsius in New York, so fatigue is surely a factor now.

Choinski responds well with a brisk hold to love.

Absolutely no messing about from Coco Gauff now. She strides back to her chair with a real air of confidence after speedily breaking to love.

The defending champion has got herself a very healthy lead.

Coco Gauff's game has got a bit of confidence about it now.

There's so much power behind the American's shots and Varvara Gracheva just can't quite deal with it.

A long way back for the French player now.

Naomi Broady
British player on BBC Radio 5 Sports Extra and BBC Sounds

I think Jan Choinski's biggest regret at the moment if he loses this match will be the break point chances that he hasn't taken.

The tally has grown larger and larger as this match has carried on.

He has had the opportunity to be 3-0 up in this fifth set.

Jan Choinski really needs to win this game to keep in touch with Roberto Carballes Baena and a double fault from the Briton comes at a bad time as he slips to 15-15.

He recovers well, however, with some strong serves to secure the hold.

Remember, this is just the second five-set match of Choinski's career after losing to Luciano Darderi at Wimbledon earlier this summer.

Coco Gauff holds her hands out in disbelief. She's frustrated after missing all three of those break points.

But here's another chance. Can she get it this time?

Yes she can! Varvara Gracheva pushes the ball into the net.

Oh dear. That's not what Varvara Gracheva would have wanted to start the second set.

Two unforced errors before Coco Gauff sends home a backhand winner for three break points.

I take a few sips of my coffee, look back and there's been another slight change of momentum as Jan Choinski brings up two chances to break back immediately.

Roberto Carballes Baena finds his first serve just when he needs it though to bring the game to deuce, before seeing out the hold.

Sealed with an ace. Coco Gauff gets the first set in Arthur Ashe Stadium.

The 6-2 scoreline makes it look like light work for the defending champion, but it's been anything but.

Varvara Gracheva failed to make the most of six break points. Gauff, on the other hand, won two of the three break points available to her. It's all about taking your chances.

Jonathan Jurejko
BBC Sport

Jan Choinski seems to be a man of his word.

Heading into his US Open main-draw debut, the British number 10 said he would leave everything out on court.

That's exactly what he has been doing.

Choinski has trailed by an early break in the third and fourth sets. Now he must fight back again in the decider...

And just like that, Roberto Carballes Baena has three break points.

The Spaniard takes them at the first opportunity as Jan Choinski steps in and spoons a forehand wide.

If this match has taught us anything though, it's don't count out the Briton yet...