An Iain Hume strike gave City a half-time lead and after the interval DJ Campbell, Alan Sheehan and Mark De Vries were all on target to put the home side four goals up before Marlon King scored Watford's consolation goal from the penalty spot in time added on.

Allen said: "It's good to get a win, but it's only three points. It's great for the players and great for the supporters.

"I'm really pleased for the players because they also work so hard."

Allen said the arrival of Iranian international Hossein Kaebi, who received international clearance on Thursday and made his Leicester debut as a second-half substitute, meant his squad was now complete.

He said: "We've now got a good, big squad of players and each and every one of them now knows they have to earn their place in the team and no one has a divine right to play."

The City boss also had harsh words for referee Anthony Taylor after a game often punctuated by yellow cards and off-the-ball incidents.

"I thought the referee was distinctly average. I couldn't understand some of his decisions, I couldn't get my head round them."

Watford manager Ade Boothroyd said Watford had something to learn from their heavy defeat.

He said: "This could prove to be our best result of the season. We earned a reputation in our first two games and perhaps turned up here today thinking everyone was afraid of us. But as Leicester have shown, they were not afraid and we got the boot up the backside our performance deserves.

"I thought we started the game really well, but you have to score goals in your dominant periods and make sure you don't give away silly goals, we didn't because their first goal was a superb strike."

After a slow start City scored on 15 minutes when Campbell flicked the ball on to Hume, who let fly from 25 yards with a shot that cannoned from the underside of the bar into the net.

The second came on 51 minutes when a half cleared Stephen Clemence free kick fell to Campbell, who guided the ball home from close range.

The home side were three goals up on 54 minutes when Clemence touched a free kick to Sheehan, whose deflected shot left the wrong-footed Mart Poom with no chance.

A fourth followed on 86 minutes when De Vries held off a defender and beat Poom with a curling shot from a tight angle seven yards out.

City could have had more, striking the woodwork twice in the second half, but it was Watford who had the last say when King scored from the penalty spot in time added on after James Chambers was ruled to have fouled King inside the area.