Arsenal scored four and missed at least six as they toyed with Watford's dreams of joining the fabled list of glorious giant-killers which has been compiled down the years of FA Cup folklore.

The Gunners' continental class made them look visitors from a different planet at times rather than just the Premier League. It was almost embarrassing the way they tore apart Watford's toiling defence time after time.

Yet from two goals ahead after nine minutes they took more than an hour to finally confirm their blatant superiority when Nigerian ace Kanu headed in a Patrick Vieira cross to make it 3-1.

And if manager Arsene Wenger had any worries at all they were contained in the myriad of missed chances his team piled up instead of notching a cricket score.

Even after substitute Dennis Bergkamp slotted into an empty net for Arsenal's fourth five minutes from the end after climbing off the bench for his familiar cameo role, gallant Watford were still not finished and Marcus Gayle's emphatic strike in stoppage time at least gave the First Division side another memory to savour.

It was possibly a sign of what was to come when Watford's Islington-born former Arsenal midfielder Paolo Vernazza gave the ball away straight from the noon kick-off in his haste to make an impression on the club that sold him last season.

And almost before the fans had settled in their seats, Wenger's team were two up. Kanu, with a shuffle past one tentative challenge and a flick through to Thierry Henry, was the creator of the first, although the predatory Frenchman looked distinctly offside as he rounded goalkeeper Alec Chamberlain to slot his 23rd goal of the season into an empty net.

But almost before Watford's protests had died down, Henry had set up a second, luring Chamberlain off his line after escaping Patrick Blondeau's sleepy attentions, and unselfishly laying on a square ball for Freddie Ljungberg to despatch.

It looked all over but pride kept Watford going and they were rewarded with a towering header from young striker Gifton Noel-Williams who massively outjumped Martin Keown and Sol Campbell to thump in Gary Fisken's fine cross in the 13th minute.

But if the 20,105 crowd thought they had a game on their hands again, Arsenal took an iron grip - simply refusing to panic at the thought that they could become the latest victims of the FA Cup's shock-littered history.

Yet though they had Watford running in circles with an exhibition of classic pass-and-move style they somehow could not administer the killer blow as one chance after another went begging.

Chamberlain soundly collected a couple of dangerous crosses and was also saved a close-range Keown header which should have been buried.

The busy keeper also distinguished himself by keeping out Keown's header after the Arsenal defender looked a certain scorer from a cross by Robert Pires, who had pounced on an error by Ramon Vega.

But Watford, with two lively wide players in Gayle and Tommy Smith feeding the tall Noel-Williams in the centre, gave the Arsenal defence some uncomfortable moments as well and Campbell had to make a superb last-ditch tackle to stop Allan Nielsen making the most of Vernazza's precise low pass into the six-yard area.

Watford's main menace was obviously aerial with another former Tottenham man, Vega, going forward to join Noel-Williams for every set-piece but it was a marauding run by the tiny Smith which almost unhinged Arsenal again in the 34th minute.

He shook off three challenges when cutting in from the right and then fired narrowly over the crossbar from the edge of the area.

Arsenal responded with another Pires-inspired raid which ended with Kanu firing over with a shot on the turn. And they should certainly have gone 3-1 up when the entire Watford back-line missed a low cross from the left and Kanu was left with only Chamberlain to beat in the 41st minute.

The tall striker dragged the ball around the keeper but left himself a rapidly-reducing angle for his close-range shot and saw it deflected into the side-netting by Blondeau.

Just before the break, Giovanni van Bronckhorst did put the ball in the Watford net after a typically marauding run by Vieira who found the Dutchman with a delightfully chipped pass but referee Alan Wiley spotted van Bronckhorst handling the ball before slotting past Chamberlain.

In the second half it was just a question of how many chances Arsenal could make - and miss. And the answer was plenty.

Henry dwelt too long on a Ljungberg cross, trying to make a good opening too perfect before being crowded out; Vieira's effort was blocked by Blondeau and then he jabbed wide when sliding in to meet Oleg Luzhny's cross.

It was approaching the comical when the otherwise brilliant Pires trod on the ball in front of an open goal after van Bronckhorst set him up.

But after a sumptuous ball out from the back by Campbell, Arsenal finally put scoring distance between them and their outclassed hosts. Kanu sprayed it out to the right and moved in to head home Vieira's cross with apparent ease.

There were still 28 minutes to go and Watford, whose first effort at goal in the second half came from Smith soon afterwards, were finally out of contention - especially when Bergkamp and Sylvain Wiltord were sent on as late substitutes for Henry and Kanu.

Bergkamp had time to roll in the fourth for Arsenal after Watford's defence had been stripped bare again but when goalkeeper Stuart Taylor could only palm out sub Heidar Helguson's cross in stoppage time, Smith worked like a Trojan to get the rebound to Gayle who slammed in a cracking if futile riposte.

Teams:

Watford: Chamberlain, Cox, Vega, Issa, Blondeau, Fisken (Helguson 79), Nielsen, Vernazza (Hand 90), Gayle, Smith, Noel-Williams.

Subs Not Used: Baardsen, Wooter, Doyley.

Booked: Fisken.

Goals: Noel-Williams 13, Gayle 90.

Arsenal: Taylor, Luzhny, Keown, Campbell, Cole, Ljungberg, van Bronckhorst, Vieira, Pires, Kanu (Wiltord 82), Henry (Bergkamp 82).

Subs Not Used: Grimandi, Upson, Stack.

Goals: Henry 8, Ljungberg 10, Kanu 63, Bergkamp 85.

Att: 20,105

Ref: A Wiley (Burntwood).