Rafael Nadal is facing three break points and saves the first with Zverev ballooning a shot into the crowd. With all the eyes of 15,000 people on a fan in the crowd, the delighted spectator grabs it one handed. Good catch, sir.

On to the second break point and Nadal's powerful cross-court forehand is just wide of an out-stretched Zverev.

Two saved, one to go. But Nadal can't wriggle out of this one and goes long as Zverev breaks back.

Who thought this was over? Anyone? Not yet. We are back on serve and it is 2-2.

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Some magnificent hitting from both players, as Zverev eventually takes charge with his two-hand backhand proving the difference in a sensational rally, as Nadal finally goes wide.

The German then takes the next point and he has a chance for a break here. 0-30.

Leon Smith
Great Britain Davis Cup captain on Radio 5 live sports extra

When you watch the movement of Zverev it is so efficient and so well balanced. He's creating opportunities because he's been very aggressive on the ball.

You get the feeling that at some point he will get another chance and then, let's see what he can do in those situations.

But the German is hanging in there. He hits down a couple of aces on his way to a service game to love.

Zverev remains a break of serve down in the deciding set.

'Come on Rafa, I want to go home' shouts someone in the crowd, but why anyone wants this to end soon is beyond me as it is enthralling stuff.

OK, those waiting for the evening session to get going may be keen for this one to be over soon.

Nadal produces a rare double fault, only his fourth of the match, but it does not matter as he jumps into a 2-0 lead. This is going to be some story if Zverev wins it from here.

Novak Djokovic's conqueror, the always superbly attired Denis Istomin, has backed up his win over the world number two with a five-set victory over Spain's Pablo Carreno Busta.

After three hours and 27 minutes it was Istomin who came out on top, sealing a 6-4 4-6 6-4 4-6 6-2 win. Very symmetrical.

The world number 117 will now face either Dominic Thiem or David Goffin in round four.

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The winner of this one will play either France's sixth seed Gael Monfils or Germany's Philipp Kohlscreiber, the 32nd seed. That one is ongoing and still in the early stages of the first set where they are at 2-2.

A perfectly sliced backhand helps Nadal move into an early 15-30 advantage off of Zverev's serve.

Nadal is just too good at the moment and he soon earns a break point. Zverev looks frustrated, wondering what can he do to stop his opponent.

He has no answers shortly after as Nadal breaks in the first game of the deciding set. He is now in pole position.

Leon Smith
Great Britain Davis Cup captain on Radio 5 live sports extra

It's been topsy-turvy from a Zverev point of view. Nadal is what he is. He's been solid but it's Zverev that can dictate what goes on in this match.

When he's aggressive and hunting the ball down, he can cause problems. He knows that and he looks pretty focused. If he can maintain his level, be the aggressor, he can create opportunities.

Zverev needs the game to stay in the fourth set and makes a bright start, winning the opening point. But Nadal throws in a serve-volley to mix things up and it is 15-15.

Nadal goes ahead but Zverev shows that, despite being 6ft 6in, he has great pace, sprinting to a drop shot for a winner that makes it 30-30.

But he is not quick enough shortly after as a Nadal forehand blurs past him to give the ninth seed a set point.

And he only needs one set point. He bolts down an ace down the centre of the court, the Spanish flags are being waved and we are down to a one-set shootout.

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BBC Two

In case you're just waking up, British number one Johanna Konta is through to the last 16 after demolishing Caroline Wozniacki 6-3 6-1, and you can watch highlights of that and the other day six action on BBC Two from 15:05 GMT.

A service game to love keeps Zverev alive in the fourth set, but he is still a break down with Nadal serving to make it two sets all.

Over at the Hisense Arena, third seed Milos Raonic has breezed through the first set against France's Gilles Simon.

It took the third seed just over 30 minutes to win the first set 6-2 and he's currently 2-1 up in the second set.

A fourth round tie with either Roberto Bautista Agut or David Ferrer awaits the winner of that match.

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Leon Smith
Great Britain Davis Cup captain on Radio 5 live sports extra

Nadal's had to dig deep. He's not played his best tennis and he's certainly not been the aggressor, but he's found his way.

I am impressed with Zverev and the way he's got his way back into the set. Even if this set escapes him, he's in a good position and playing the right way.

But Rafael Nadal is showing the skills that have seen him win 14 Grand Slams. He holds his serve and is 5-2 up in the fourth set.

How much does Zverev have left? He is being forced around the court as Nadal's power is proving dominant.

Who will prevail? The youthfulness of Zverev or the experience of Nadal? A wild return from Zverev goes well long and signs of tiredness are creeping in.

Then we have something special. Nadal serves wide, Zverev gets a racquet to it, the drop volley from Nadal is not the best and Zverev tries a lob. But Nadal, at the net, jumps high, spins round and gets the contact, with his back facing the net, for a spectacular winner. Wonderful. And the crowd love it.

But Zverev still is alive in this game and takes the next point for deuce.

Leon Smith
Great Britain Davis Cup captain on Radio 5 live sports extra

It's a great match up, the older generation against the younger generation.

We're trying to see where Rafa is, as well as where Zverev is as a contender. We know he has long-term potential, but is that potential about to realise itself sooner than we think?

Zverev saves the first break point via a challenge with Nadal only fractionally denied.

The Spaniard gets another break point chance for what would be a 5-1 lead, but for the second time the teenager hangs in there.

He bangs down an ace and, despite a big scare, saves two break points to win the game. Hard-fought.

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We have now moved into the fourth hour of the match and this could all come down to which player has the greater engine.

Zverev has game point but a sliced dropshot attempt from the back of the court is misjudged and clips the top of the net to take us to deuce.

He then slaps a half volley into the net. Nadal break point.

Leon Smith
Great Britain Davis Cup captain on Radio 5 live sports extra

I think Zverev looks really composed. He knows he's good enough to beat Nadal.

He knows he has the game to do it and he knows everyone is talking about it. Everyone is talking about the future, but it could be now that it all starts.