Jeff Tarango
Former professional tennis player on BBC Radio 5 live sports extra

If you hit a drop shot and it bounces before it hits the net, you should probably go and change your racquet. I mean, it's obviously not you, it's the racquet...

Third time lucky for Serena!

She eventually breaks as Sevastova hits a shocker of a drop that doesn't even reach the net.

Not only is the Latvian playing Serena Williams here, she's also got a 23,000-strong crowd against her. There's no doubt who they're supporting.

Serena has sorted those forehand problems out. Her husband is on his feet as she brings up another break point.

Two drop shots from Sevastova. One brilliant. One into the net. We're at deuce.

We've seen that one before. Serena gobbles up a short second serve by pummeling it for a winner down the line.

From 0-30 Sevastova fights her way back level but then the Latvian miscues.

Here's Serena's first break point. The noise levels lift in the crowd again.

Russell Fuller
BBC tennis correspondent on 5 live sports extra at Flushing Meadows

She didn't look anything like Serena in those first two games. But she managed to turn it around in that last game. I am not surprised by the way Sevastova has started though. I am not surprised that she has adapted and settled well in what is the biggest moment of her professional career.

Sulaimon Adelekan: Up by midnight in Lagos, Nigeria to follow my favourite Serena Williams. Please make it count!

Sevastova loves this slice. Again and again she turns to it on the backhand side.

Serena's big sis Venus is watching on. She looks pensive but not overly worried. She's seen this all before.

It's the Serena forehand which is faltering. Again she goes long for what must be the fourth or fifth time. That takes us to 40-30 and the crowd try to lift the American. Better. She wins the next point to get on the board.

Jeff Tarango
Former professional tennis player on BBC Radio 5 live sports extra

Serena needs to drop the anchor. She is not reading it very well yet. It just looks like her legs aren't warm.

The crowd are trying to kick-start Serena's challenge. They cheer when the American forces an error from her opponent.

But Sevastova is outmaneuvering her opponent right now. She's pulling her in and then flicking the ball past the 23-time Grand Slam champion at the net.

This is some start from the player making her Slam semi-final debut.

Jonathan Jurejko
BBC Sport at Flushing Meadows

That's dampened the atmosphere somewhat. The biggest thing the crowd had to cheer in the opening game was Serena correctly challenging that line call.

Anastasija Sevastova is scurrying left and right on the baseline. She's using her slice and trying to retrieve everything.

She thinks she has her service break when a Serena forehand is called out but hawkeye overturns the decision. It was just in.

No luck for Serena this time. She goes long. It's the Latvian who breaks in the opening game.

Williams made a slow start against Karolina Pliskova in the quarter-finals, falling down an early break. She misses three groundstrokes here in this opening game.

15-40.

Two break points to Sevastova.

Jonathan Jurejko
BBC Sport at Flushing Meadows

Ear-splitting cheer from a half-full Ashe when six-time champion Serena is introduced.

A partisan atmosphere. Sevastova must feel like she's Wayne Rooney playing at Anfield.

Serena to serve.

Ready...

Play.

Jeff Tarango
Former professional tennis player on BBC Radio 5 live sports extra

I didn't think Serena would be moving so well since having a baby but she's really impressed me. I think she's even surprised herself how well she is moving.

Russell Fuller
BBC tennis correspondent on 5 live sports extra at Flushing Meadows

Serena Williams is playing as well as she has done since her comeback. Her tennis has been on another level here.

The umpire calls time.

These two have never met before. Sevastova is a tricky player, much more slender than Williams with a less powerful game.

But could she cause problems to the great American? We're about to find out.

David Law
BBC Radio 5 live sports extra commentator at Flushing Meadows

They have made a great call putting the roof on so soon. The forecasting equipment here must be off the scale because they get it right every time. They know what is coming. We heard some pretty extreme flashes of thunder on our way up to the commentary court.

Adding to the music gig feel, Serena Williams is wearing a leather jacket over her light blue tutu at the coin toss.

The American wins it.

On come the lights. Screams from the crowd. Let's get ready to rummmmbllllllllle.