But back to deuce we go as Madison Keys is unable to reach a clever body shot from Aryna Sabalenka.

The American pushes the next point into the net before hitting another unforced error.

Keys will really regret not making more of that if she ends up losing here.

Advantage Madison Keys. She has another break point as Aryna Sabalenka's lob misses the mark.

Aryna Sabalenka lets out a scream as she saves the break point by drilling a backhand past Madison Keys. Deuce.

We've just passed the two hour mark on Arthur Ashe Stadium.

Aryna Sabalenka's longest match of the tournament had been one hour 18 minutes.

The Belarusian finds herself under a bit of pressure once again as she slices a forehand wide and gives Madison Keys another break point.

This match isn't ending anytime soon. These two look like they could continue into the early hours of the morning in New York.

Aryna Sabalenka raises a fist as she breaks back straight away.

Now it's Aryna Sabalenka's turn for two break points.

Jonathan Jurejko
BBC Sport at Flushing Meadows

Kudos to the Ashe DJ... again. Had a superb fortnight so far.

We're after midnight so on comes Abba's Gimme Gimme Gimme.

"Gimme gimme gimme a man after midnight..."

More than a few are jovially singing along.

She doesn't get it at the first time of asking as Aryna Sabalenka whips home an ace.

But it's second-time lucky for Madison Keys as the second seed pushes another forehand long.

Is that the decisive moment?

Madison Keys benefits off two more long forehands and a double fault from Sabalenka. Three HUGE break points for the American.

Aryna Sabalenka is playing a lot more aggressively now and she looks the more energetic of the two players.

That said, it could be too much. The Belarusian second seed overhits a couple of forehands to gift Madison Keys the hold.

Jonathan Jurejko
BBC Sport at Flushing Meadows

Even this semi-final going into a deciding set could not prevent hordes of spectators heading home just before midnight in New York City.

Streams of people filed down the stairs from the upper tier while Keys received treatment.

Those who remain are gripped.

Image source, Getty Images

A fairly straightforward hold for Aryna Sabalenka.

We remain on serve in this third set. Who is going to blink first?

Fantastic play from Madison Keys. She chases down every ball before playing a cross-court drop shot that fools Aryna Sabalenka.

Even Sabalenka can appreciate that, giving Keys a wry smile and a little round of applause.

The American holds.

Winner. Winner. Ace. A tidy start for Aryna Sabalenka.

But hold on, she follows that up with two misses.

A strong serve down the middle from the second seed stops us from going to deuce.

A huge hold for Madison Keys.

Aryna Sabalenka hits two unforced errors either side of a Keys' backhand winner.

Image source, Getty Images

A break point straight off the bat for Aryna Sabalenka in this third set.

Madison Keys is back, but she returns with some strapping on her thigh. Could that prove to be an issue for her in the decider?

Let's hope not. This match has been full of twists and turns, so hopefully that can continue.

Aryna Sabalenka is back on the court and she looks like a different player compared to the one we saw in that first set and in the opening half of the second.

She's pacing around calmly as she waits for Madison Keys to return.

You can't help but feel that the second seed, who will become the new number one on Monday, has the momentum on her side now.

Could Madison Key's dream be over even earlier than anticipated?

She heads down the tunnel for a medical timeout. The American appears to be struggling with a hip issue as she receives attention from the physio.

Aryna Sabalenka also heads to the locker rooms for a bathroom break.

Image source, Getty Images

Madison Keys is on a downward spiral. She just couldn't get any hold of that tie-break whatsoever.

She was so close to making her second-ever Grand Slam final but it looks like that dream could slip away very quickly.

Aryna Sabalenka is back in this match with bang.