Hornets remain in promotion picture
Matej Vydra's superb volley helped keep Watford on the trail for automatic promotion as they recorded a 2-0 victory over a spirited Millwall side, who sank further into relegation trouble.
Millwall were on top for much of the first half but a stunning hit from Vydra saw the Hornets take in a slender advantage at half-time.
Aiden O'Brien was a constant menace for the hosts - who had an early penalty shout turned down - but Watford were far too clinical, as Adlene Guedioura slotted a vital second goal shortly after the break.
Millwall keeper David Forde was called into action in the first minute, doing well to deny Troy Deeney after the striker had broken the offside trap.
The Lions quickly gathered momentum and despite some promising approach play - with O'Brien at the heart of much of it - failed to create any meaningful opportunities.
And the home side had a legitimate penalty shout after Ben Watson bundled over of Ed Upson, as the midfielder jinked in from the right, but that went unpunished.
After Watford weathered the storm, Vydra produced his moment of inspiration by volleying in from just outside the box in the 26th minute.
Forde was helpless as the Czech thumped the ball into the far corner from Ikechi Anya's cross.
Millwall, playing with renewed hope of survival after a first win in 10 on Good Friday, then squandered a golden opportunity when Martyn Woolford failed to pick out O'Brien lurking unmarked two yards from goal.
The hosts also ended the half in the ascendency as Jimmy Abdou's scuffed shot was well saved by Heurelho Gomes.
Millwall huffed and puffed as they had in the first-half, but created few chances of any note. They came closest to boosting their slim survival hopes when O'Brien robbed Matthew Connolly of possession, but Gomes saved well.
In the 54th minute, Anya - as he did for Vydra's opener - created Watford's second. The Scottish winger combined with Troy Deeney to outfox Shaun Cummings and Sid Nelson before squaring for Guedioura, who tucked away a six-yard tap-in.
It was a goal that Watford's second-half performance deserved, as they overcame Millwall's superiority before the break to showcase the quality that puts them on the brink of the Premier League.
They twice came close to adding to the lead, as first Vydra then Odion Ighalo ran free on goal. Forde managed to gather the ball at Vydra's feet and then saved agilely from substitute Ighalo.
Avoiding defeat would have equalled their longest unbeaten run of the season at four games, but the Lions more than likely need to go without a loss in all five of their remaining fixtures to stand any chance of beating the drop.