Aryna Sabalenka really does possess some incredible power and, as Annabel says, Emma Navarro is struggling to deal with it on the pacey hard court.

Navarro needs to dig in here to stay in the set and she finds a way to hang on a little longer.

An ace earns the hold.

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

Aryna Sabalenka's fast start was important. She has just stepped it up a gear, she has tightened the screws, cut out the unforced errors and she is just overpowering Emma Navarro at the moment.

Navarro has definitely got the attention of the crowd but I think Sabalenka has gone up a gear. I think she has had to.

Image source, Getty Images

An unforced error from Aryna Sabalenka gifts Emma Navarro a look at break point but the American fires into the net and we're at deuce.

Sabalenka seizes the opportunity to take back control and goes on to hold.

The Belarusian is on the verge of claiming this first set.

Emma Navarro recovered well after being broken in her first service game - giving Aryna Sabalenka a taste of her own medicine - can she do the same again here?

We get our first real rally of the match - 13 shots in total - with the full range of strikes on show.

Navarro lobs from the baseline and then has to go into full defence mode as Sabalenka finds a return before eventually hooking a winner across court.

30-30.

Image source, Getty Images

Emma Navarro finds a forehand winner to save the first.

But she can't hold out any longer as Aryna Sabalenka gets a break again in this first set.

Is that going to be a momentum shifter?

Aryna Sabalenka is starting to move through the gears now and she has three shots at break point after digging out a beautiful cross-court serve return.

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

Image source, Getty Images

Aryna Sabalenka is looking less comfortable than I have seen her for the whole tournament.

This is looking like the old Sabalenka. The last shot she hit was only just in. It's quite evident from the first few games that we have seen this is going to be a tussle.

Emma Navarro makes Aryna Sabalenka work for the hold but an emphatic forehand down the line is enough to do the job for the Belarusian.

We've got a match on our hands here.

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

Image source, Getty Images

That was impressive. Emma Navarro is playing the best that she can possibly play right now.

It's early in the match right now but at the moment she is playing the better tennis.

Aryna Sabalenka is rattled.

A huge roar as Emma Navarro shows the aggression she spoke about pre-match with a serve and volley to lead 15-0.

A lovely forehand puts her 30-0 up and it's quickly 40-0 as Aryna Sabalenka fires long.

A double fault slows the momentum briefly but a fine leaping backhand down the line sees the game out for Navarro.

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

Image source, Getty Images

Emma Navarro is very, very tactically astute. She is having to make those quick decisions on the court, she's got that kind of brain.

She'll love the challenge of what she has to do to overcome this power game of Sabalenka.

Emma Navarro comes back fighting and has two attempts at breaking back.

Aryna Sabalenka defends the first with an ace but Navarro gets over the line at the second attempt.

That'll settle any nerves as the crowd springs into life.

There are still a lot of empty seats around Arthur Ashe stadium.

Emma Navarro would have been hoping for a strong backing but the crowd aren't playing their part just yet.

Aryna Sabalenka fires a lovely backhand down the line to get a first look at break point.

And she takes it.

Are we seeing some nerves from home hope Emma Navarro in her first Grand Slam semi?

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

Image source, Getty Images

Aryna Sabalenka is up against a great athlete and a very good thinker. Emma Navarro is highly intelligent.

Both previous matches between the pair were tight. I just feel like Sabalenka at the moment is the one to beat at these Championships.

Regardless of whether Iga Swiatek was in it, she beat Swiatek quite convincingly at Cincinnati on a very fast court and that was quite something.

I feel like her whole overall game has gone to a different level.

So much talk about Aryna Sabalenka's serve in the build up to this match and she lays down an early marker by holding to 15.

Warm ups done and we're ready to get under way in this first of two semi-finals at the US Open.

Aryna Sabalenka will serve first.

Featuring at this stage of a Grand Slam is becoming very familiar for world number two Aryna Sabalenka.

The Belarusian has reached at least the semi-finals on eight of her last 11 appearances at Grand Slam events.

Speaking to Sky Sports before stepping on to court, Sabalenka said: "I'll try to do my best to get this win.

"She [Navarro] moves really well and does smart things.

"We've played two tough matches against each other and I'm looking forward to playing her tonight."

Jeff Tarango
Former American tennis player on BBC Radio 5 Sports Extra and BBC Sounds

Emma Navarro has exactly the temperament and game to beat Aryna Sabalenka.

Sabalenka is all firepower. She will blast away and she is going to overpower Navarro for a time. How long that will last, we don't know.

Navarro will come back at her and start nipping at her heels, she's got the best wheels on tour and she has no pressure on her, never will.

I would say Navarro is almost unstoppable on her rise on tour, she is just getting better and better and better.

Sabalenka should win this match but the drama of it with New York completely behind Navarro who was born here it is going to be fun.