Phew! What a night/morning.

Here's a reminder of how Victoria Azarenka reached her first Grand Slam final in seven years.

And there she will play Naomi Osaka, who beat Jennifer Brady in another superb match.

Let's catch up on some sleep and do it all again tomorrow, yeah? Excellent.

Men's semi-final day. Here's what is in store. See you then, 21:00 BST sharp.

Incredible story is Azarenka reaching a Grand Slam final again. She could barely buy a win last year and said she almost quit the game because she wasn't enjoying it.

Added to that have been tough personal issues, being locked in a custody battle over her son Leo who she gave birth to in 2017.

But since returning after the restart she has won 11 matches in a row. One more over Naomi Osaka on Saturday will give her a third Grand Slam title.

Amazing.

More from Victoria Azarenka, speaking to Amazon Prime: "It feels amazing, I'm so happy to be in the final, it is really exciting and I can't wait to play in the final. Today was a great day and I knew I would have a lot of fun.

"Mentally it is one of the strongest comebacks I've done because I had to get myself out of really big trouble.

"At this stage of a Grand Slam against Serena you know she is not going to give anything so in that way it is one of the best matches I've played."

Azarenka has been here before, of course. Twice she has reached a US Open final before and both of those were among those 10 losses to Serena (in 2012 and 2013).

Third time lucky?

David Law
BBC Radio 5 Live Sports Extra tennis commentator

This is the woman who thought that retirement beckoned but her personal life settled down and her professional life is on the rise once again.

Victoria Azareka: "I have been working on finding a calm mind and keep the body going. I need to find energy to climb out of the hole and it wasn't easy. Hopefully it inspires women to go after their dreams, they can do anything. I am so excited to play Naomi, she plays incredible, she is super strong so I have to stay strong to get the most out of it."

Intensity and energy, combined with calm and poise. Azarenka got the balance absolutely perfect after that wake-up call in the first set.

She had never beaten Serena Williams in a Grand Slam match. That unwanted record is off her back at the 11th attempt.

Never mind... she lands a first serve which Williams' backhand can't deal with.

Match point Azarenka...

Uh oh... double fault! 30-30...

An 89mph winner from Williams cracks a dent in the Azarenka defence... 15-30.

Can Azarenka hold it together?

Another anguished cry from Williams as she battles gamely but can't return a stretching backhand at the end of a nine-shot rally... 30-0.

Russell Fuller
BBC tennis correspondent

Anything could happen here...

Smart play from Azarenka who exposes Williams' lack of movement because of that ankle injury... 40-30.

But Williams drags herself over the line with a gutsy hold.

Over to you, Vika...

Breathing space. Azarenka lumps a backhand long for 40-15..

Positive start for Williams as she slams away a volley for 15-0 and then bats back a forehand winner for 30-15...

Here we go. Serena Williams is serving to stay in the US Open...

And there is the answer. More clean hitting, with purpose and precision, sees Azarenka move 40-0 ahead and she clinches the game two points later. Williams goes for broke with a backhand down the line and sprays it well wide.

Azarenka has never beaten Williams at a Grand Slam. She's 0-10. Has she got the belief to get over the line?

This game will tell us...

Exactly what Williams needed. A relatively comfortable hold to love. The only blip was a double fault which stalled her to 40-15, getting over the line when Azarenka dumps a backhand into the net on a second serve.