Leon Smith
GB Davis Cup captain on BBC Radio 5 Sports Extra 2 and BBC Sounds

Katie Boulter plays a high tempo and high risk game but, when you haven't had that bank of matches, then getting that balance of when to really let go of the ball versus when to just take a touch off it becomes difficult.

She isn't far away in this match though, she just needs to rein it in a little bit. The last 10 minutes of that first set was much more like the Katie Boulter we would expect to see.

It's very much advantage Iga Swiatek already.

She quickly converts the first of two break points on Emiliana Arango's serve to put herself a break up in the first set.

Despite falling 0-30 down on her own serve, a powerful forehand gets her back in it and she is able to win four points in a row to press home her advantage.

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Sonay Kartal has stepped things up at the start of the second set. There's a bit more punch and power behind her groundstrokes and it's paying dividends for the British number three.

Beatriz Haddad Maia goes long on the first of two break points and Kartal has an early break.

Katie Boulter misses her first serve and puts herself under serious pressure on break point but she misses the second serve too and that hands over the break of serve for Marta Kostyuk at the earliest opportunity.

Katie Boulter still looking a little off it in the early stages of set two.

She moves to game point but Marta Kostyu works her way to deuce then earns herself a break point.

Leon Smith
GB Davis Cup captain on BBC Radio 5 Sports Extra 2 and BBC Sounds

Katie Boulter didn't start that first set particularly well and Marta Kostyuk was definitely in control in those opening stages.

Boulter did get that break back and we did think she was starting to find her rhythm, but there are still just a couple of errors creeping in. Kostyuk is doing a brilliant job out there, she is serving well and she is going after it.

The key difference is on second serves, with Boulter down at 25% of points won on second serves compared to Kostyuk at 50%.

On Louis Armstrong Stadium, 10th seed Lorenzo Musetti has dropped the first set against big-serving Frenchman Giovanni Mpetshi-Perricard, losing it on a tie-break.

That neither player was able to conjure up so much as a break point in the first set was no shock but perhaps more surprising is that 6ft 8in Mpetshi-Perricard, who broke the speed record at this year's Wimbledon with a serve clocked at 153mph, has only served four aces so far.

It's been a difficult summer for Italian Musetti since he had to pull out of the French Open semi-finals with injury - he's won just one match since then. He probably wouldn't have wanted an opening-round encounter against world number 37 Mpetshi-Perricard, who reached the semi-finals at last week's ATP event in North Carolina, and now has a first win at the US Open in his sights.

After losing her previous two service games, that's just the start Sonay Kartal would have wanted in set two.

She gets to 40-0 in double-quick time and Beatriz Haddad Maia nets on the second game point.

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Marta Kostyuk closes out the first set with a decent serve.

Katie Boulter with it all to do on Grandstand Stadium.

Emiliana Arango is helped by four misses from Iga Swiatek on the way to a hold.

The Colombian is on the scoreboard but a powerful forehand in the opening point from Swiatek sets the tone for her own service game, and despite another double fault, it's a comfortable hold for the Pole.

We remain on serve in this one.

Marta Kostyuk gets lucky with a net cord to earn set point but some smart play from Katie Boulter, dragging Kostyuk into the net and forcing her into a split slide takes us to deuce.

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Leon Smith
GB Davis Cup captain on BBC Radio 5 Sports Extra 2 and BBC Sounds

That is seriously good tennis from someone whose had a really rough year. She doesn't look like someone who is lacking confidence. She's playing with a lot more freedom just now.

Her footwork is spot on and she's playing very aggressive, not being tentative with any of her shots.

A hold to love in arguably her most convincing service game of the match so far and that's enough for 18th seed Beatriz Haddad Maia to clinch the first set of her first-round match against Great Britain's Sonay Kartal in 42 minutes.

Leon Smith
GB Davis Cup captain on BBC Radio 5 Sports Extra 2 and BBC Sounds

I would imagine Katie Boulter was a bit nervous coming into this match because she hasn't played a huge amount of matches this summer.

So her confidence is a little bit low, but if she can start to just feel the ball and the strings well then it will make a big difference for her.

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A superb serve down the T levels things at 15-15 as Marta Kostyuk tries to serve out the set. But a double fault puts Katie Boulter 15-30 ahead.

The two Britons are mirroring each other at the moment. Katie Boulter and Sonay Kartal broke serve at almost the same time, now they've lost their serves at almost the same time too.

Kartal saves the first break point with a fine forehand winner, but Beatriz Haddad Maia bosses the next rally to make it three breaks of serve in a row on Court 12.

The Brazilian is serving for the first set.

Ouch. Brutal.

A double fault hands over the break to Marta Kostyuk.

All that hard work to break back is immediately wiped out and Kostyuk is one game from taking this first set.

Leon Smith
GB Davis Cup captain on BBC Radio 5 Sports Extra 2 and BBC Sounds

Good on Katie Boulter! She was definitely more aggressive on the ball during that game and she is just rushing her opponent.

One of her many strengths is the ball speed that she has. She has got big strikes that can rush opponents, so I really like that tactic in these quick conditions.

If she can continue to hit the ball hard and through the middle of the court, I think she will get some success.

Iga Swiatek manages an ace and a double fault but is able to get the job done.

She takes the first game of this match 40-15.

Katie Boulter finds herself in a spot of bother again here on serve.

Marta Kostyuk does really well to chase down a drop shot at the net but Boulter's return is walloped wide.

That's two break points for the Ukrainian.