Everton romped to victory to keep their push for the Uefa Cup on course and leave Watford in desperate trouble.
Everton's Manuel Fernandes celebrates his goal with Tim Cahill
Manuel Fernandes stabbed home his first goal for Everton after 23 minutes when Watford keeper Richard Lee fumbled Tim Cahill's shot into his path.
Andrew Johnson doubled Everton's lead two minutes later from a disputed penalty after he was challenged by Jay DeMerit and Adrian Mariappa.
Substitute Leon Osman added a spectacular third in injury time.
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Everton were able to recall fit-again Johnson after he missed the midweek defeat against Tottenham - and he was a pivotal figure as the visitors ran the first 45 minutes.
Watford keeper Lee almost gifted Everton the lead after 17 minutes when Cahill's shot squirmed from his grasp but he recovered to just stop the ball crossing the line.
He redeemed himself with a fine save from Johnson's header, but he was fault when Fernandes poked Everton in front.
Lee fumbled another shot from Cahill but this time there was no escape as Fernandes just beat Johnson to the loose ball to score.
And Everton doubled their lead from the spot.
Johnson tumbled under a challenge from Mariappa and DeMerit, with referee Lee Mason pointing to the spot instantly.
Watford fans howled their disapproval at Johnson, who has been at the centre of diving accusations this season but there appeared to be clear contact and the Everton striker rammed home the spot-kick.
Cahill then wasted a perfect opportunity to put Everton out of sight after 28 minutes when he was played in by Johnson but he lifted his finish over the bar with only Lee to beat.
James Beattie then delivered a perfect demonstration of why he has failed to score a goal in open play this season, with an awful miss on the stroke of half-time.
Johnson, the first half's outstanding player, set up Beattie right in front of goal only eight yards out but he blazed his finish embarrassingly off target.
Watford boss Aidy Boothroyd made a double change for the second half, sending on Tamas Priskin and Lloyd Doyley for Malky Mackay and Darius Henderson.
And Priskin gave Watford their best moment after 57 minutes when his 25-yard shot flashed just inches wide.
He was a threat again three minutes later when he met Steve Kabba's superb cross but headed wide, with Everton keeper Tim Howard beaten.
Priskin was the focal point for Watford's best period of the game but Everton broke the shackles for Mikel Arteta to fire across the face of goal after 72 minutes.
Everton rounded off a comfortable win when Osman curled in a superb finish from 25 yards in the dying seconds.
Watford boss Aidy Boothroyd:
"A mad five-minute spell cost us. It was a mixture of naivety and the need for our players to be 100% for every game.
"When at 100% we will give anyone a game outside the top ones but when we are not at it we look like a team that can do a lot better.
"There's 30 points to play for and we are where we are for a reason. We have not won enough and we have to do that."
Everton boss David Moyes on striker Andy Johnson:
"I think he frightens defenders to death. He is very quick. I would select him for England.
"It was great to see the way the players went about their job. There was a real determination.
"I was disappointed not to go in three or four ahead at half-time. It was difficult after the break but we got there in the end."
Watford: Lee, Mariappa, DeMerit, Mackay (Doyley 46), Stewart, Smith, Francis, Mahon, Bouazza (McNamee 78), Henderson (Priskin 46), Kabba.
Subs Not Used: Loach, Williams.
Booked: DeMerit, Smith.
Everton: Howard, Neville, Yobo, Lescott, Naysmith, Fernandes (Osman 81), Carsley, Cahill, Arteta, Johnson (Vaughan 77), Beattie.
Subs Not Used: Wright, Hibbert, Anichebe.
Goals: Fernandes 23, Johnson 25 pen, Osman 90.
Ref: L Mason (Lancashire).