Image source, Getty Images

The lowest set average by either man was 93.27 by Zonneveld in set three. That gives you an indication of how high the quality has been here.

But this could be the killer, as Jonny Clayton brings out another massive D8 to break throw.

Hold here, and he's into round four.

There have been two matches at this year's World Championship that have needed a sudden-death leg to decide a winner.

Scotland's Alan Soutar, in round one, and England's Justin Hood, in round two, have both won at the last gasp.

If this deciding set gets to 5-5 in legs, the winner of the 11th leg will go through to the fourth round.

That is Niels Zonneveld's second 11-dart leg in this match. This is the biggest match of his career, and he has brought the best performance of his life. It has included TWENTY-FIVE 140s.

But Clayton has the first throw, sets up a 44 finish - and bangs the third dart into D8, followed by a fist pump.

Now onto 11 180s for Clayton, to open the fourth leg. Phenomenal.

He sets up a 96 finish, before a 140 from Zonneveld moves him to 81.

Ooh, a messy visit of 26 from Clayton, big chance for Zonneveld...

TAKEN! An 11-darter ensures we are going the full distance.

We have now had 16 180s in this match, 10 of them from Clayton.

Make that 17! Zonneveld pings in his seventh. Sensational.

He's loose at the doubles, but with Clayton way back Zonneveld is able to hold.

Image source, PA Media

Niels Zonneveld will not go quietly. He opens leg two with a 180.

A fourth perfect dart... and a fifth! But the sixth is into single 19.

Still Zonneveld is really fighting, and although Clayton has just hit his 10th maximum of the match, the underdog cleans up an 11-dart leg.

Tremendous.

Stuart Pyke
Commentator on Sky Sports

Niels Zonneveld is possibly playing the match of his life, because he's playing better than he did in beating Michael Smith.

But he's still behind!

Niels Zonneveld's average? 99.60

Jonny Clayton's average? 99.63.

Nothing between them.

But could this be decisive - Clayton sets up a 48 finish on Zonneveld's throw, and the Dutchman can't check out 100.

Clayton sweeps up, and that could be a key break.

The first four legs in his fifth set have all been won in 15 darts or fewer. Electric darts.

Jonny Clayton has the throw in the decider, and gets to a 101 finish with Zonneveld a ton back.

Clayton is just outside the D12, and though Zonneveld applies pressure with another 100-plus visit, the fifth seed cracks in the double at his next turn.

Jonny Clayton has raised his game here. He bangs in the 15th 180 of the match so far.

He needs 164, with Zonneveld lurking on 96.

Clayton gets the two trebles... but again the bull is missing.

And Zonneveld cleans up. Terrific match.

Jonny Clayton has been matched by Niels Zonneveld so far, and is now trying to up the pace.

Both men are on 121 - Clayton misses, then Zonneveld nearly lands in the bull but rests in the 25.

Clayton holds, just.

Suddently neither player is able to hold their throw.

Zonneveld is nowhere after a poor 42 visit, and Clayton nearly lands a brilliant 140 checkout.

The Welshman returns to nail D10, and we are back on serve.

Niels Zonneveld has picked up where he left off, earning three darts at tops on the Jonny Clayton throw.

He lands in single 20, but bags D10 and breaks again.

That's four legs on the spin for Zonneveld.

On we go. The winner here faces an unseeded player, Andres Harrysson or Ricardo Pietreczko, in the last 16.

They open up this evening's session, which will get under way just after 19:00 GMT.

Glen Durrant
Former Premier League champion on Sky Sports

Jonny Clayton was looking good and looking at taking control, but Niels Zonneveld is right in the mix.

Jonny knows he's in a game.

We are up to 11 180s in this match - seven of them from Jonny Clayton - and 21 140-plus visits. 15 of those have come from underdog Niels Zonneveld.

Both men are averaging around 50% for their checkouts too.

One of the most high quality and closely fought matches of the tournament so far.

Image source, PA Media

That previous leg saw a 126 checkout from Niels Zonneveld, the biggest of the match so far.

Jonny Clayton can't respond with a 155, so Zonneveld needs 78 for a clean sweep in this set.

And he finds it! These two excellent players cannot be separated.

A look of frustration from Jonny Clayton after a 44 visit, followed by a 77 from Zonneveld. Suddenly the big scores have deserted both men.

But it is Zonneveld who rises from the mire first, following a T19 with bull to break the Clayton throw.

Niels Zonneveld will draw level if he keeps hold of his throw in set four.

He gets a bounce out at the worst time possible, heading for a second T20 as he aimed for a 144 checkout.

But Zonneveld is made of pure tungsten, and sees it out.