The tension builds further when Amanda Anisimova's shot is called long but it appears to be in.

The chair umpire has stopped play and is on the phone.

It's deemed incorrect and Anisimova closes in further.

The chair umpire urges the crowd to remain silent during the rallies as this tie-break comes to a crescendo.

A couple of holds keep Amanda Anisimova in it for now but Naomi Osaka has a further three set points and is back on serve.

Naomi Osaka pulls further clear with her fifth ace of the match.

The four-time Grand Slam champion raises her fist to celebrate as she gets set point.

A double fault from Amanda Anisimova and then the American puts into the net to hand over a double mini-break.

Naomi Osaka is closing in on the first set.

A ripping backhand gets Amanda Anisimova to 15-30 but Naomi Osaka comes battling back with a backhand winner of her own for 40-30.

Anisimova gets under her return from deep behind the baseline and on we go to the tie-break.

Amanda Anisimova's first serve has been inconsistent throughout this match so far but she finds a bit of joy just when it matters.

A couple of big serves get her to 40-30 and she wraps up the hold with a sweeping forehand.

The American is guaranteed at least a tie-break.

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Amanda Anisimova can't take the first but she gets it at the second attempt and in stunning fashion too.

A ripping forehand winner return back down the line.

I've already given up trying to predict how this set might conclude.

Ah.

A double fault is not how Naomi Osaka would have wanted to get started.

Osaka puts wide and then long to hand over three break back points.

We've seen a few nerves on show from Amanda Anisimova in this semi-final - how will the 24-year-old hold up in this pressure moment?

Pretty well.

Anisimova plays some lovely groundstrokes - sending Naomi Osaka across the baseline - before sealing a hold to 15.

Over to Osaka to serve for the set.

Naomi Osaka finally gets over the line with her third ace of the match.

Amanda Anisimova will serve to stay in the opening set.

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Naomi Osaka kisses the baseline with her forehand and it catches out Amanda Anisimova - she can only return into the net.

But Anisimova whips a stunning forehand winner into the corner for third deuce.

It's the same again. Osaka earns advantage but Anisimova drags it back to deuce once more.

Tense stuff now.

Not this time.

Naomi Osaka digs in her heels to get to deuce.

Amanda Anisimova has come out swinging.

The American has two break points.

Arthur Ashe Stadium - with the roof closed - looks like a disco with music blaring and lights flashing at the change of ends.

No peace for the players.

Amanda Anisimova shows her first signs of emotion with a huge roar when getting back to advantage.

Naomi Osaka can't get the following serve back over and Anisimova gets back within touching distance.

Leading 15-30, Naomi Osaka has a great chance to earn break point when Amanda Anisimova steps up to the net but she sends a passing shot long.

Osaka hits a beautiful backhand to get to deuce but follows up into the net.

Anisimova has a golden chance to strike into space down the line for the hold but overcooks the shot.

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Much better from Naomi Osaka with a hold to 15.

A little bit of scoreboard pressure on Amanda Anisimova in the opening set now.

It's long from Amanda Anisimova and Naomi Osaka is back in control.

A messy start to this semi-final.

Oh no.

Just when it looked like Amanda Anisimova had settled into this semi-final, the American gives up two break points.

Amanda Anisimova gets it.

Game on!