Millwall underlined their promotion potential with an emphatic victory at Vicarage Road to send Watford crashing to their first league defeat in eight games.

Gianluca Vialli's men were torn apart as Millwall claimed all three points in clinical fashion.

Watford hit the post through Tommy Smith after 23 minutes but otherwise were rarely a threat until Heidar Helguson scored a consolation nine minutes from time.

Millwall could have been ahead when a missed header by Ramon Vega bounced in front of Tim Cahill, but he shot straight at Alec Chamberlain.

Vega, who received a booking in each half, was given his marching orders in injury time to add to Watford's woes.

Cahill was not to be frustrated long.

After 31 minutes he met Steven Reid's cross with a firm header into the Watford net.

Home keeper Chamberlain then saved from Reid just before the interval.

But the visitors doubled their lead 13 minutes into the second half.

A half-cleared free-kick fell to Marc Bircham whose shot was blocked and Richard Sadlier picked up the loose ball, resisted a couple of challenges and fired home.

After 68 minutes Watford were caught by a quick counter-attack which saw Reid running clear before driving the ball low between Chamberlain's legs.

Substitute Nordin Wooter, who had seen a header tipped over the bar earlier, set up a consolation goal for Watford and Helguson drove the ball in low from 12 yards.

However Millwall scored a fourth a minute from time when Neil Harris was allowed to come inside and call a shot beyond Chamberlain from just inside the penalty area.

Then Vega fouled Sadlier to receive a second yellow card to complete a woeful day for Vialli and company.

Watford: Chamberlain, Blondeau, Issa, Vega, Robinson, Fisken, Vernazza, Nielsen, Gayle, Smith, Helguson. Subs: Baardsen, Hyde, Wooter, Noel-Williams, Cox.

Millwall: Warner, Lawrence, Nethercott, Dyche, Ryan, Reid, Cahill, Bircham, Livermore, Sadlier, Claridge. Subs: Harris, Ward, Gueret, Green, Bull.

Referee: C Foy (St. Helens).