Zheng Qinwen is making a match of this now.

She's started to get a foothold in the rallies to cause Iga Swiatek some problems, and she wraps up the game as the Pole can't get a forehand over the net.

Anastasia Potapova wasn't behind for long in the second set - she has broken back against Mirra Andreeva to level it at 2-2.

Image source, EPA

Zheng Qinwen earns another break point but Iga Swiatek snuffs it out with a superb backhand winner down the line.

The Pole just can't get over the line here as a long forehand gifts a third break point of the game to Zheng, and this time she makes it count as Swiatek goes long again.

That's one back for the Chinese world number 121.

Back to deuce as Iga Swiatek wins a rally, before the Polish eighth seed brings set point.

Zheng Qinwen saves it as Swiatek goes wide with a backhand.

The crowd are doing their best to give Zheng Qinwen a boost by cheering extra loudly when she wins a point.

This is the best she's done on Swiatek's serve so far as the game heads to deuce and she brings up break point as the Pole finds the net.

The volume level on Arthur Ashe Stadium goes up that little bit more...

Image source, Getty Images

Mirra Andreeva still looks a bit frustrated but she has made a positive start to set two after losing the first set to Anastasia Potapova.

The Russian teenager broke Potapova in the opening game and then escaped from deuce to hold serve for a 2-0 lead.

Daniela Hantuchova
Former world number five on BBC Radio 5 Sports Extra

Even though she is 5-1 down, I have to say I'm liking what Zheng is trying to do in the rallies.

If Iga Swiatek drops her intensity even a little bit, as we're seeing right now, this match has the potential to go the distance.

Zheng has the groundstrokes to overpower Iga.

Daniela Hantuchova
Former world number five on BBC Radio 5 Sports Extra

There has been a lot of excitement. The women's field in particular, it's in such a healthy, strong position.

It's one of those tournaments where anyone can take it from here.

Image source, Reuters

That will do Zheng Qinwen's confidence a world of good as she finally gets on the board.

She wraps the game with with a lovely backhand volley which Swiatek can't reach in time as she sprints in towards the net.

Swiatek will now serve for the first set.

Iga Swiatek is well on top so far but a large part of it is down to Zheng Qinwen's unforced errors.

She's hit eight so far to Swiatek's two.

On serve, the Polish eighth seed sees out a comfortable hold to love and she's now one game away from the first set.

Daniela Hantuchova
Former world number five on BBC Radio 5 Sports Extra

It seems like the fatigue is starting to kick in for Zheng, unfortunately.

The adrenaline will have been pumping after that comeback win in the last round but she just can't seem to get the tiredness out of her legs.

Zheng Qinwen's underwhelming start continues as she offers Iga Swiatek another break point before a double fault sees the Polish eighth seed win the game.

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Anastasia Potapova lets out a huge roar as she takes the first set of her fourth-round match against Mirra Andreeva on Louis Armstrong Stadium.

It looked to be heading for a tie-break, but Andreeva's frustration was starting to grow in the closing moments of the opening set and she was broken to love by Potapova.

Andreeva, the French Open champion, would be the highest seed to exit the women's draw so far if she is beaten today.

Zheng Qinwen works Iga Swiatek around before stepping inside the court to put away a forehand winner.

She's still making too many unforced errors however, and a couple more loose forehands bring up two break points for Swiatek.

Zheng fights back well, with Swiatek unable to take advantage of a second serve, and the game heads to deuce.

Daniela Hantuchova
Former world number five on BBC Radio 5 Sports Extra

I think Iga Swiatek is enjoying that not too many of us picked her as a favourite coming into the tournament.

Image source, Reuters

That's better from Zheng Qinwen as she steps into the court and slaps away a forehand winner.

Iga Swiatek fights back by getting the better of two rallies and she secures the hold as Zheng can't get a serve over the net which was fired towards her body.

Zheng showed signs she's starting to settle in that game there but Swiatek is deservedly up 3-0.

Russell Fuller
BBC tennis correspondent on BBC Radio 5 Sports Extra

Swiatek has had a fairly serene passage through the draw so far with three straight-sets wins.

Whereas, Zheng had to go through qualifying and I don't know whether the comeback from 5-0 down in the third set against Madison Keys in the last round will have drained her or inspire her, but it was her fourth three-setter in a row.

Image source, Reuters

Iga Swiatek has settled straight away while Zheng Qinwen has not found her range yet.

A couple of loose shots bring up three early break points for Swiatek, and the Pole makes them count at the second opportunity as Zheng overcooks a forehand.

Daniela Hantuchova
Former world number five on BBC Radio 5 Sports Extra

It's not been easy for Zheng. Injuries are the most difficult part of being a professional athlete but it gives you so much more humbleness, perspective and appreciation.

Here she had to go through the qualifiers and I think it will be a good lesson for her so when she gets back into the top 10, which is where I think she belongs, she'll be much more appreciative of it.

Iga Swiatek comes out on the top in the first rally of the match before Zheng Qinwen can't keep a first serve in play.

Swiatek wraps up a hold to love as Zheng then spoons a forehand wide.

Confident start from eighth seed Swiatek.