0-30.

Breakback mountain?

Not yet as Sev produces another one of her beautiful drops which Stevo just gives up on chasing.

15-30.

30-30.

Game Sevastova as the defending champion makes another error.

Followed by a groan around Arthur Ashe.

Another...another unforced error from Stephens - a wide forehand which shouldn't have been wide.

0-15.

A double-hander from the green then hits the top of the net.

0-30.

"I must punish you further," Sevastova doesn't say, as she sends Stephens out wide.

0-40.

Three break points.

One saved.

A hopeful cheer from the crowd...

The good work is partly undone with a double-handed backhand against the net.

The Latvian then produces a stunning passing backhand winner to seal the game

Top, top work Sevastova.

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

Stephens is down on her haunches wondering what's going on. The whole of America is looking forward to seeing her play Serena Williams in the semi-finals but it doesn't look like it's going to happen at this point.

Another superb drop is met with a lone "whoop" from the crowd. Most of the spectators are supporting the American in the orange.

But it's the Latvian in the peach who is the star on the main court so far.

An ace brings up game point.

40-0.

Hang on.

40-15.

40-30.

And then Stevo produces an angled return that licks the top of the net and lands in.

Deuce!

Remarkable really!

Stephens is back.

She needs to bring her 'B' game never mind her 'A' game.

Image source, Getty Images

Sev takes the first opportunity with a lovely angled forehand as Stevo barely moves.

The defending champ walks off the court for a quick break and gestures to someone or other about something en route.

Probably about the fact she's been a mess in the first set.

Having commented on the unforced errors. Sev actually leads those stats 15-11.

Make that 15-13 as Stevo finds the net from mid-court.

0-30.

0-40.

Three set points.

30-0.

Sev keeps gesturing to her coaching team, almost every time she makes an error.

30-15.

Stevo then makes yet another error - it looked like she lost sight of the ball there.

40-15.

Game.

This match has yet to ignite.

15-0.

15-15 as Stephens goes long.

The American once again goes long - it's all very lacklustre from the defending champion, so far.

15-30.

Stephens then makes a side-slap smash as Sev loops one up towards that sphere of hot plasma.

40-15.

Stephens eventually holds. Important hold.

It's break-point three Stephens, but the American makes another mistake.

There seems to be a bright star beaming from the bottom of the middle of the net.

Follow that star!!

Advantage Sev.

The Latvian then produces another stunning angled drop which Stephens returns but Sev is in the right position to win the point and hold.

Stevo looked for glory with an angled forehand but it found the net.

Deuce.

Advantage Stephens again.

Now, here's a chance - an relatively simple backhand smash.

Noooo!! it finds the net.

15-15.

Great low sliced returns from Stevo frustrates Sev, so much so that she sends her shot wide.

15-30.

30-30.

Sev then goes wide with forehand.

Break point for Stevo.

Can she break back?

Pressure on Stevo here - another unforced error.

Two break points - the crowd try to encourage their home player.

She duly doesn't oblige by planting a drop against the net.

Broken.

Sev is having a chat with the umpire - not exactly sure what the issue is.

Possibly over the issue concerning the moving fans - it's definitely not Wimbledon. In the defence of the paying public, it's a huge arena. That's the only defence.

Sloane is back in the sun.

15-15.

She goes wide with a shot into the shadows.

15-30.

Stevo goes long and the game is finally over.

Sev holds but that was a tough little runaround in this intense heat.

Can the pair keep this up?

I have been tetchy with the spectators who don't know when to move and sit down between games - this time they are actually doing it during the game.

Seriously?

Advantage Sevastova before Stevo brings up deuce six with a 83mph forehand.

Devastating.

Saved again.

But the American brings up break point four with another forehand into the corner.

Saved once more as Stephens finds the net with her return.

Sev then throws Stevo out wide - her opponent cannot find accuracy with her return.

Advantage Sevastova after Stephens loses her challenge.

The 28-year-old makes yet another error.

Break point two.

But she pulls Stephens to the net and saves with a backhand.

Is that the sound of break point three? Yes, as Stephens smacks down a winner.