Watford came back from a goal down to avoid an FA Cup upset at the hands of Stockport County.
Mackay was in clinical form for Watford
David Poole slotted in a shot from the edge of the area to put the visitors into a shock lead.
But Malky Mackay turned in a shot at the far post to level before a Tommy Smith's strike put the Hornets ahead.
Mackay slid in at the far post to notch his second before an error by keeper James Spencer allowed Moses Ashikodi to score a goal on his Watford debut.
Watford's sought-after Ashley Young had been left on the bench for the game and the Hornets made a nervous start.
Hornets keeper Ben Foster is normally an assured presence in goal but he raced out of his goal to collect a loose ball and only cleared it straight to Poole, whose 30-yard effort was on target but was blocked by Mackay.
606 DEBATE: Your thoughts on Watford's win
Watford had two goals disallowed before Poole latched on to a Tony Dinning pass to put his side ahead.
But, rather than inspiring Stockport to a win, the goal only served to make the Hornets more determined and their efforts were rewarded as Mackay and Phillips struck
Stockport had their moments as they battled away for an equaliser and Stephen Gleeson headed just wide from a Poole cross.
But the visitors found their opponents too strong as Mackay and Ashikodi extended Watford's lead.
Watford manager Adrian Boothroyd on goalscoring striker Moses Ashikodi:
"Moses will always be a nuisance for defenders, because he looks to play on their shoulders.
"He scored a goal that most players would not have bothered chasing down, but he did and got his reward.
"It is good to get four goals. We took our chances, and hopefully this can push us on to win games in the second half of the season."
Stockport boss Jim Gannon:
"We are very disappointed, because we just did not play well. We lost the game because we conceded poor second-half goals.
"We didn't do the things we had worked on in training.
"Michael Malcolm was very poor. Maybe the talk of a transfer has affected him," added Gannon, who seems set to lose his forward to Werder Bremen.
Watford: Foster, Mariappa, DeMerit, Mackay (Doyley 84), Stewart, Smith, Francis (Diagouraga 62), Bangura, McNamee, Henderson (Young 68), Ashikodi.
Subs Not Used: Lee, Powell.
Goals: Mackay 30, Smith 48, Mackay 76, Ashikodi 82.
Stockport: Spencer, Clare, Poole (Le Fondre 69), Owen, Tunnicliffe, Gleeson, Dinning (Rowe 81), Taylor, Griffin, Dickinson, Malcolm (Bramble 46).
Subs Not Used: Deasy, Raynes.
Goals: Poole 23.
Ref: L Probert (Gloucestershire).