US Open tennis: Cerundolo upsets Fritz, Zheng stuns Keys, Swiatek in action – live

So in the fourth round it'll be Fritz Cerundolo v Cobolli Blockx. No 14 Learner Tien and No 17 Jakub Mensik, who play in the night session, are now the highest seeds left in that quarter of the draw.

Cobolli double faults at the worst possible time, because it hands the break to Blockx, who will serve for the match at 5-3 in the fourth. And the Belgian nervelessly blasts his way to 40-0 … before finishing the French Open runner-up off with an ace out wide! The shocks keep on coming. The 21-year-old Blockx is through to the last 16 of a grand slam for the first time, having never even played at a major before this year, and Cobolli, having perhaps expended too much mental and physical energy in his first and second-round comebacks, has departed. “I definitely didn't think this would happen so quick,†says a surprisingly calm Blockx.

A huge cheer on Arthur Ashe, as Coco Gauff grabs the first game against Spain's Cristina Busca. It's louder than you'd expect given it was only the opener, but this crowd is desperate for an American win after the whitewash so far today. Surely Gauff is in strong enough form to get through this? And yet … we said the same about Fritz. Nothing is guaranteed on this wild Saturday.

Swiatek suddenly remembers who she is, breaking back Bouzkova – who won only five games against her at this year's Australian Open – and then holding to haul herself level in the second set at 7-6, 4-4.

Meanwhile Karen Khachanov, who took out an ailing Felix Auger-Aliassime in the second round, is 4-3 ahead in the first set against France's Benjamin Bonzi, and Dane Sweeny, who knocked out an out-of-sorts Lorenzo Musetti on Thursday and is the last Australian standing in the singles, is 5-4 down in the opener, with Italy's Luciano Darderi serving for it.

And that next one for Cerundolo will most likely be against Blockx, the Belgian who sounds as if he should be part of some brand colab, who's close to pulling off an upset of his own, now 6-7, 6-3, 6-0, 3-1 up on Cobolli. But Cobolli won from two sets down in the first round, so this deficit is niente to the Italian … and Cobolli breaks back from deuce with one of his nuclear forehands! As Bouzkova breaks Swiatek for a 4-2 lead in the second set! Today's drama shows no signs of abating.

So how did Cerundolo turn it around? “I don't know,†he says. “He was playing way better than me in the first two sets. In the third I started to get into it, step by step, and in the fourth and fifth I played really good tennis. Taylor is a top player, he's played in the final here, so winning, my first time on Arthur Ashe, it's fantastic. I hope you enjoy, I know I'm not the local one, sorry, I try my best, hopefully I can get you all on my side in the next one.â€

Now it's Cerundolo's turn to miss a gimme of a forehand and Fritz has a glimmer at 0-30. Fritz can't put any pressure on Cerundolo on the next point, but a lengthy rally plays out at 15-30 … before Fritz fires long by some distance. 30-all. Will it be break point or match point? Match point, because Cerundolo slams down an unreturned serve out wide! And the Argentinian takes out the ninth seed when Fritz batters a backhand beyond the baseline! For only the second time in Cerundolo's career, he's come from two sets down to win, and Fritz, the man whom I'd tipped to be the leading American this fortnight, is out. What a gut punch for Fritz at his home tournament. He'll be seeing that 4-3 game in the final set in his sleep for many a night. Fritz, Keys and Anisimova are all gone on this Saturday of shocks.

Fritz must recover from that disappointment fast … but Cerundolo steps into the court, crunching another fizzing forehand, and Fritz is left doing the splits and facing a 15-40 deficit. And Fritz's shoelace has broken, so he'll be given a moment to fix that, just to add to the drama. When they resume, Cerundolo's shot clips the tape on the first break point … trickles over invitingly for Fritz to bury it … but Fritz flaps his forehand into the net!!! And from three break points up on Cerundolo's serve, Fritz is now a break down, and Cerundolo will serve for a place in the fourth round at 3-6, 4-6, 6-3. 6-4, 5-4!

But let's focus on Fritz v Cerundolo, because this may be a potentially decisive moment after three and a half hours, with Fritz having taken seven points on the spin and a point away from serving for the match at 4-3 and 0-40 on the Argentinian's serve. But Cerundolo drowns out the sound of nearly 24,000 Americans with some HUGE serving. And then he cracks an unreturned forehand to get to his advantage! And Fritz is screaming to the skies as Cerundolo secures the game! Clutch.

Keys' defeat, having led Zheng 5-0 in the third set and had a match point, comes two days after Keys saved five match points and came from 5-2 down in the decider to win – so tennis really does know how to give and take.

And now Fritz is looking to avoid following Keys and Anisimova, his fellow Americans, out of the tournament on this Labor Day weekend – which given the way he obliterated his first two opponents was not a sentence I expected to be typing today. And Cobolli is reeling, too, now 6-7, 6-3, 6-0 down to Blockx – though Andreeva is through and Swiatek has finally wrested control against Bouzkova, taking the first-set tie-break 7-3.

Thanks Niall. So I haven't missed much while I've been away, have I? Oh.

Time to hand back to Katy, who will guide you through the rest of the afternoon session's action.

Flavio Cobolli is in trouble, now 5-0 down to Blockx in the third set, and set to slip 2-1 behind in sets. Bouzkova couldn't take the chance to serve out the set – Swiatek breaks for a third time to set up a tie-break.

Marie Bouzkova breaks Swiatek to lead a gruelling first set 6-5, and she'll try to serve out the first set, which has lasted almost an hour. Back on Ashe, Fritz fights through a tough service game to edge 2-1 ahead in the decider.

There's some British interest in the men's doubles, with Arthur Fery (born in Paris) and Jonathan Paris (born in London) in first-round action. They're taking on Ivan Liutarevich and Anirudh Shandrasekar.

Cerundolo wraps up the fourth set, and we're heading to a decider on Ashe. Alex Blockx has hit a purple patch against Cobolli, reeling off five straight games to win the second set and break early in the third.

Job done for the No 5 seed, who scrapes through a second-set battle, winning the tie-break 7-5. Next up for her: Anastasia Potapova, who eliminated Amanda Anisimova earlier today.

Swiatek and Bouzkova are locked at 3-3 in the first set, with Blockx and Cobolli on the same score in set two. On Court 17, Mirra Andreeva needs to win a tie-break to secure victory over Bartunkova.

Taylor Fritz has his arms outstretched, unsure how to regain the initiative against an opponent who is moving and hitting much better than before. At least his trusty serve keeps him in the set, but he needs to pose Cerundolo more problems. The Argentinian leads 5-3 in the fourth.

Cerundolo breaks to edge ahead in the fourth set, and this has become an unexpectedly testing encounter for Fritz. Elsewhere, Nikola Bartunkova – the world No 34, and Czech No 6 – is 6-5 up in the second set, with Andreeva serving to force a tie-break.

Swiatek immediately breaks back, and they're back on serve at 1-1, with 15 minutes required to play out two games. On Ashe, Fritz edges 2-1 up in the fourth set, but we're still on serve.

Cobolli takes the first set! He prevails 7-4 in the breaker against Blockx. Iga Swiatek and Marie Bouzkova have begun on Grandstand – and the Czech player has claimed an early break.

Mirra Andreeva has won the first set 6-2 against Bartunkova with the second set on serve at 2-2. Elsewhere, Alex Blockx has fought back to force a first-set tie-break with Cobolli.

While all that was happening, Francisco Cerundolo started a comeback of his own. From two sets and a break down, the Argentinian has won the third set and is causing Taylor Fritz a few problems.

“Any sign of a dramatic Zheng comeback? No, is the short answer†– me, 35 minutes ago. I was wrong, and Zheng moves on to a last-16 meeting with either Iga Swiatek or Maria Bouzkova, who are up next on Grandstand.

“I always believed [I could win], I just kept fighting,†says Zheng, who found serving at 5-4 down the toughest moment. She talks about her injury layoff – “the worst few months of my career†– and says “hard work has paid off†for her and her team.

On second serve, Keys looks to clip the line with a cross-court shot … but misses. Zheng Qinwen has won from 5-0 down, breaking Keys' serve three times in a row and saving a match point at 5-1 down. She looks elated, Keys can't wait to get out of there. How on earth did she lose that match?

From 5-0 down, Zheng is serving for the match. Will the pressure pendulum swing? Keys edges ahead with some nimble net work, but can't keep her forehand down with Zheng now feeling the heat. Match point Zheng …

Flavio Cobolli has sped out of the blocks against, er, Alexander Blockx – the Italian leads 4-2 in the first set. But we're staying on the Grandstand for now …

Zheng breaks Keys again! Madison Keys makes a better start here, the first serve speeding up, but Qinwen Zheng is locked in, turning the rallies in her favour – and when Keys misses a desperate effort down the line, she breaks again. Three in a row, six games in a row, and now she'll serve for the match.

It's five games in a row for Zheng as she controls her service game – and now Keys must serve again at 5-5. Zheng was ranked world No 4 just over a year ago, but is currently No 121 after a run of injury problems – and had to qualify for this tournament.

Over on Stadium 17, No 5 seed Mirra Andreeva has taken an early break against Nikola Bartunkova, who is unseeded but ranked 34th in the world, so not far off.

The nerves are all too obvious from Keys, whose first serve slows to a crawl as she slides 0-40 down. Keys saves the first break point, but eventually goes long and Zheng is 5-4 down, back on serve and back in the game.

Zheng moves 40-0 up and has Keys throwing her arms up in frustration – but the American rallies to deuce, only for Zheng to grind out the hold. Keys will serve for the match again, and the pressure's on …