Annabel Croft
Former British number one on BBC Radio 5 Sports Extra and BBC Sounds

Sinner hit a shot there right at Alcaraz's body - you do not see that very often. Perhaps he was trying to get rid of some adrenaline in his body.

A jaw-dropping level from Alcaraz. We saw a little bit of everything from him - mixing up the paces, serve and volley.

Image source, Getty Images

Well, that was impressive.

Brilliant serving - Alcaraz lost just three points on his own serve in that set - coupled with that fizzing forehand and a brilliant variety of shots and the Spaniard is in control.

Sinner has some answers to find.

A bit of a smirk on the face of Sinner as Alcaraz makes another reaction return at the net and pulls it off.

The Spaniard has three set points.

Annabel Croft
Former British number one on BBC Radio 5 Sports Extra and BBC Sounds

Another service game where Sinner looked under pressure.

It will be interesting to see when Sinner starts looking towards his camp. He normally keeps his emotions in but when he looks across there, you will know he is starting to feel uncomfortable.

Alcaraz is in the driving seat.

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Alcaraz serving for the set after 34 minutes. Sinner is going to have to find some answers in the second set.

As we know with this match-up, anything can happen.

Another miss! This time at the net from Sinner.

The defending champion is somewhat bemused. Alcaraz takes a double break lead. He has been brilliant so far.

Oh my word. Alcaraz is just getting to everything while Sinner is making uncharacteristic errors.

The Spaniard comes into the net and reaches the drop shot but Sinner's passing return drops wide of the line.

Another massive forehand from Alcaraz brings up two break points for the Spaniard.

Annabel Croft
Former British number one on BBC Radio 5 Sports Extra and BBC Sounds

It is one thing to think about using short slices but it is another thing to produce it.

Roger Federer had that shot nailed - you drop it short because then your opponent is inside the baseline and it gets them into a difficult position.

Such good play from the Spaniard.

A very strong hold to love for Alcaraz. He holds to love thanks to a couple of big serves and a couple of ripping forehands.

The Spaniard still has that break advantage.

Marion Bartoli
Former Wimbledon champion on BBC Radio 5 Live

Image source, Getty Images

You can see the constant aggression that Alcaraz is bringing which is different to his play at Wimbledon. It has taken Sinner by surprise.

It is clear to see that it will take a very special level from Sinner to come out on top today.

Annabel Croft
Former British number one on BBC Radio 5 Sports Extra and BBC Sounds

Alcaraz is throwing the slice shot into the mix. He did not get as much knife into the ball as he usually does and then that did upset his own rhythm.

Sinner did well to get back on track in that service game.

Alcaraz shows power with a backhand down the line then incredible touch and feel to drive into the net and play a deft little drop shot for 0-30. A cheeky little grin as he heads back to the baseline tells you how he feels about that one.

But Sinner regroups, winning the next four points to take the hold.

Annabel Croft
Former British number one on BBC Radio 5 Sports Extra and BBC Sounds

Alcaraz is keeping Sinner guessing. He is bringing his mix and artistry into this match.

You can hear that the crowd know they are witnessing some incredible talent from these players.

Jonathan Jurejko
BBC Sport senior tennis reporter at Flushing Meadows

Still plenty of empty seats - especially in the upper tier - after the delays caused by the extra security measures.

The change of ends after the third game brought an influx of people, but clearly a huge number are stranded outside.

Every spectator has to go through an airport-style scanner outside of Ashe, meaning they have to empty pockets into a tray, go through a full-body scanner and be searched if the detector beeps.

Sinner goes for the lob - slightly bizarre decision - but Alcaraz punishes him with the overhead smash volley.

The Italian has notched up seven unforced errors so far.

Alcaraz drags Sinner into the net with the drop shot and the top seed goes long. We're already seeing the Spaniard's greatest hits and he takes another hold.

Marion Bartoli
Former Wimbledon champion on BBC Radio 5 Live

Image source, Getty Images

It is interesting to see how much Alcaraz is going for every single second serve return and is putting so much pressure on Sinner to make his first serve.

You can see that the game plan from Alcaraz is to go on the offence whenever there is a slightly more neutral ball.

Annabel Croft
Former British number one on BBC Radio 5 Sports Extra and BBC Sounds

Image source, Getty Images

The versatility that Alcaraz has in his wrists to neutralise the point and absorb the pace of the ball is incredible defence.

Sinner is having to work hard for his service games.

As was the case in Sinner's opening service game, Alcaraz draws level at 30-30 but this time the Italian works hard to withstand the pressure and takes the hold with a solid forehand.

Annabel Croft
Former British number one on BBC Radio 5 Sports Extra and BBC Sounds

Neither player is wasting a single opportunity to thump the ball. Both will push each other physically and mentally. I don't understand how they will play at this level for possibly five hours.

There are a few backhands from Alcaraz which seem to cause problems for Sinner.

Sinner just looking a little off it and he can't do anything with an Alcaraz serve into the body.

A crunching forehand follows on the next point before the slice wrongfoots Sinner and that's the hold.

Break consolidated, what a start.