Here we go then.

Emma Raducanu, serving for a place in the third round of the US Open.

Polish seventh seed Iga Swiatek lost the first set to France's Fiona Ferro, went a break up in the second but has now been pegged back.

She's struggling on serve but leads 5-4 with Ferro serving next.

Well held. Zhang forces Raducanu to serve for the match.

Laura Robson
Former British number one on BBC radio

It seems like Zhang had that one spurt of energy but now it's gone again.

Zhang, serving to stay in the match, can't afford any more mistakes now.

A volleyed forehand pulls the Chinese player level to 30-30 as Raducanu threatens to wrap things up with another break.

Emma Raducanu appears to be way, way calmer than most of us watching from afar!

She barely stops for breath as an ace confirms a cool hold to love for a 5-3 lead.

Laura Robson
Former British number one on BBC radio

For the first time I'm starting to feel a little bit nervous.

Zhang has got so much experience, she can sense exactly what is going on at the other side of the net. I think this interesting times for Emma, how she comes out of the changeover. Maybe she's way calmer than we are!

Now then, can Raducanu just steady things here and hold?

She doesn't want to give Zhang any more confidence.

World number one Ashleigh Barty is in good shape. She raced to a 6-1 opening set lead over Denmark's Clara Tauson and they are level at 3-3 in the second.

Elsewhere, Polish seventh seed Iga Swiatek has work to do. She lost the first set to France's Fiona Ferro but is a break up in the second, leading 4-2 on serve.

Laura Robson
Former British number one on BBC radio

That is the first bit of stress we've seen from Emma. A little bit of tension.

A much improved Zhang Shuai does enough to see out the game.

She's a set and a break down, but is now within striking range in this second set.

Raducanu misses a first couple of break point chances but a third presents itself.

Net. Once again Zhang holds her nerve to force an error from the Briton and the game rumbles on.

Zhang looked lost a few games ago but is giving this a good go now, however Raducanu moves 15-30 up with a backhand winner and then makes deuce.

And now it's break point to Raducanu...

Much better from Zhang, who takes her opportunity to claim a first break of serve in this match.

Raducanu remains a break of serve clear, however.

Image source, Reuters

That's a decent response from Zhang. From 40-15 down, she forces deuce - and a fine backhand sets up a break point!

Laura Robson
Former British number one on BBC radio

I think Emma is at that really nice age where you have no fear. She's not thinking who she is going to face in round three, she is just focused on this match.

Image source, Reuters

An ace makes it 30-0 to Raducanu but Zhang takes charge of the next point before putting away a volley.

It's just relentless from the teenager though. Zhang is bullied into an error and Raducanu now has game point for a 5-1 lead...

Image source, Getty Images

Too soon to start looking ahead? Maybe for Emma, but not for us.

Sara Sorribes Tormo is currently beating Hsieh Su-wei 6-1 3-1 on court 12, so it could very well be the Spaniard who would face Raducanu in the third round should she get the job done here.

Zhang withstands a fightback from the Briton to take her first game of the second set

Zhang Shuai is beginning to look beaten here. A slack attempt at a return seals a hold to love for Emma Raducanu, who is now just two games away from a straight-set victory.

Russell Fuller
Tennis commentator on BBC radio

This is a masterclass.