Stefano Okaka scored his first two Watford goals as they moved up to seventh in the Premier League with a 3-2 victory over Everton at Vicarage Road.
The Italy international opened his Hornets account with a spectacular back-heel on 36 minutes, cancelling out Romelu Lukaku’s 17th-minute opener.
Sebastian Prodl hit his first goal of the season to give Watford the advantage early in the second half before Okaka doubled his tally on 64 minutes to put the game beyond the Toffees.
Lukaku grabbed a lifeline for Ronald Koeman’s men four minutes from time but there was to be no way back for the Merseysiders, who have won just one of their last 10 league games.
Meanwhile, Watford's first victory over Everton since 1987 sees them arrest a two-game losing streak and leapfrog their opponents in the process.
Missing the suspended Roberto Pereyra, Mazzarri was pleased to welcome Miguel Britos and Valon Behrami back into the Watford side after they missed last week's loss at West Brom.
Koeman, meanwhile, drafted in Gerard Deulofeu to replace the injured Yannick Bolasie, and the Spaniard was an early menace on his first league start since mid-October.
Occupied by Deulofeu's exuberant start, a puzzled Watford defence was carved open by Gareth Barry's first-time through ball as Lukaku was presented with the simple task of slotting the visitors ahead on the quarter-hour mark.
Watford had two chances to peg the visitors back immediately, but Britos' wide header and captain Troy Deeney mis-control let the Everton defence off the hook.
But the hosts were soon level thanks to a touch of class from Okaka who, having escaped Ashley Williams, nonchalantly flicked Nordin Amrabat's cross home to endear himself to the Watford faithful.
One so nearly became two on 41 minutes but, distracted by Seamus Coleman's attempted clearance, Deeney sliced Adlene Guedioura's deep cross horribly wide from close range.
Everton had the ball in the Watford net at the start of a cagey second period, but Leighton Baines' effort was rightfully ruled out, with Coleman offside in the build-up.
Two goals in five minutes then swung the game firmly in Watford's favours. First, a minute after heading a chance over from close range, Prodl steered Jose Holebas' fine delivery past a stricken Maarten Stekelenburg from close range.
The Dutch goalkeeper was then helpless to prevent Okaka from doubling his tally with a glancing header as Watford ruthlessly punished hesitancy in the Everton defence.
The Hornets then embarked on a resilience defence of their lead as Everton toiled for a route back into the game, which came with four minutes remaining when Lukaku stooped to head substitute Aaron Lennon's cross beyond Heurelho Gomes.
Everton then had a penalty claim waved away as Britos escaped punishment from referee Anthony Taylor for climbing over substitute Enner Valencia, but it proved to be too little, too late as the visitors failed to ease the pressure on their manager.
Player ratings
Watford: Gomes (6), Zuniga (6), Prodl (7), Britos (6), Holebas (6), Guedioura (6), Behrami (6), Capoue (7), Amrabat (8), Okaka (9), Deeney (8).
Used subs: Kabasele (n/a), Janmaat (5), Watson (5).
Everton: Stekelenburg (6), Coleman (5), Baines (5), Williams (4), Funes Mori (4), Barry (5), Gueye (5), McCarthy (5), Deulofeu (5), Mirallas (4), Lukaku (7).
Used subs: Barkley (5), Lennon (5), Valencia (4).
Man of the Match: Stefano Okaka