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Jannik Sinner cruises through another service game.

But we are still on serve in this third set.

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

I really feel for Vit Kopriva. You have to feel sorry for the guy because he is playing great tennis.

He is a very good player with very good hands. He is talented, he hits the ball well from the back of the court, he moves brilliantly on the baseline - but all of that literally doesn't matter in this match.

Jannik Sinner is almost saying 'well I can do what you can do better' in almost every single area. He has completely neutralised him.

If Jannik Sinner was worried about his energy levels after suffering a virus recently, he hasn't had to worry about depleting them much in this match.

Vit Kopriva's first serve has often been below 100mph and Sinner is just gobbling them up to get straight on the front foot in rallies.

But the world number 89 does manage to hold his opening serve of the third set, something he didn't achieve in the first two sets.

The crowd get mildly excited as Vit Kopriva plays a drop shot and then lobs Jannik Sinner in a well-worked point.

But this match is proving pretty routine for the defending champion, who holds to take first blood in the third set.

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

There is no sense at all that a comeback is about to begin here. There was barely even a cheer when Jannik Sinner closed out the second set, especially because it was on a double fault.

I would say there are a few people wondering out of the stadium now to go and stretch their legs, but I would say the majority are staying in here because they know this is going to be done and dusted soon.

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Vit Kopriva ends up flat on his back trying to chase down another fierce groundstroke from Jannik Sinner, which brings up two set points.

It's pretty symbolic of the match so far for the Czech player, who then double-faults to put the world number one two sets up with just an hour played.

There's a minor stir as Jannik Sinner gets the trainer out during the changeover. But it turns out he just wants a loose bit of thread cutting off a plaster he's got on one of his fingers.

Another service hold is then completed with an ace, Sinner's fifth of the match.

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

It always feels like Jannik Sinner has so many more gears that he can move through, but he always puts out a really disciplined performance.

It is always about looking ahead for him and conserving his energy. He wants to get through these early matches as efficiently as possible.

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Jannik Sinner comes up with a brilliant leaping forehand cross-court winner, and even a tweener, although Vit Kopriva does manage to win the point.

The world number one even tries a tweener but Kopriva does well to smash it away to save a break point.

But there's no stopping Sinner, who breaks again.

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

Vit Kopriva isn't playing poorly here, he is actually playing very good tennis and playing well by his standards, but the problem is you just get absolutely nothing from Jannik Sinner.

For example, if you hit a good shot then your feedback gets skewed because an even bigger shot comes right back at you.

Vit Kopriva may be being outclassed but he's showing plenty of positive body language and is trying to be aggressive.

He gets to 0-30 on Jannik Sinner's serve but the world number one immediately slams the door, winning the next four points with the minimum of fuss.

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

If Vit Kopriva can just stay within touching distance at the start of this second set, it will change the rhythm completely.

Jannik Sinner was just off and away in the first set. He looked so relaxed and loose.

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Let's get you up-to-date with some of the results so far on day three.

Tenth seed Lorenzo Musetti recovered from a set down against Giovanni Mpetshi Perricard to win 6-7 (3-7) 6-3 6-4 6-4 and book his place in the second round.

Things were more straight forward for 27th seed Denis Shapovalov who took just over two hours to win in straight sets 6-4 6-4 6-0 against Marton Fucsovics.

Suzan Lamens (bt Valerie Glozman 6-4 6-2) will take on Iga Swiatek (bt Emiliana Arango 6-1 6-2) in round two after both players won in straight sets.

Kopriva's serve is not the most powerful but he finds his first ace of the match to hold serve to love.

This is better from the Czech debutant.

Sinner wraps up another comfortable hold with his fourth ace.

This could be over pretty quickly.

Apart from a white cap, Sinner is dressed in what I believe is officially called orange but I'd describe the colour more as rust, something he isn't showing today. There's certainly no sign of any lingering ill effects from the virus that forced him to retire from the event in Cincinnati recently.

Kopriva double-faults to give Sinner an early breaking opportunity in the second set, which the Italian immediately capitalises on.

Abigail Johnson
Commentator on BBC Radio 5 Sports Extra and BBC Sounds

This is quite a tall order for Vit Kopriva because he has actually played in this event three times previously, each time through qualifying, and every single time he has lost in the first round. He doesn't have a single win to speak of at Flushing Meadows.

So going out onto Arthur Ashe Stadium and being asked to challenge the world number one is very much a tall order.

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Jannik Sinner races to 40-0 up but Vit Kopriva manages to save three set points with some gutsy defence.

But the world number one takes the first set on his fourth opportunity when Kopriva goes long with a forehand.

Just over half an hour gone, and Sinner is firmly in charge.

There's a sympathetic cheer as Vit Kopriva finally gets on the board.

Now he just has to recover that double break...

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We've only had 19 minutes of play and Sinner is already 5-0 up.