"It's been a good week," Mackay said. "My daughter Francesca who is just two weeks old was here. She was my lucky charm."
Eight wins in their last nine games have lifted Adrian Boothroyd's side to within seven points of Sheffield United in the second automatic promotion spot. Dave Jones, the Cardiff manager, said he thought Watford and Leeds are guaranteed a finish in the top six, and the evidence of Saturday suggested there is a vast gulf between Watford and the teams scrabbling for what Jones would see as the two remaining play-off slots.
The fear for Mackay is that, as has happened in the past two seasons, the club he might take to the Premiership will find no use for him there. "I didn't have much choice with Norwich," he said. "I was sold. At West Ham, Alan Pardew wanted me to stay but he told me I would not be playing in every game, so he said he wouldn't stand in the way of me leaving. Maybe this time I will get to play in the Premier League."
Boothroyd expressed a pre-game fear that the hunter would become the hunted, but there was never any danger of that. Mackay hit the bar and had an effort cleared off the line, and just as Watford were thinking it would never come, the breakthrough finally arrived after 69 minutes, as Mackay, a magnet for the ball, converted Hameur Bouazza's cross at the back post.
Jeff Whitley's unlikely equaliser suggested Cardiff might somehow escape with a point, but Marlon King capitalised on a weak Ricardo Scimeca backpass to snatch a deserved winner two minutes from time.
Goals: Mackay (69) 1-0; Whitley (77) 1-1; King (88) 2-1.
Watford (4-4-2): Foster; Doyley, Mackay, DeMerit, Stewart; Eagles (Chambers, 90), Mahon, Spring, Bouazza (McNamee, 83); King, Young. Substitutes not used: Chamberlain (gk), Chambers, Diagouraga.
Cardiff City (4-4-2): Alexander; Ardley, Purse, Cox, Barker; Koumas, Scimeca; Whitley (Weston, 85), Ledley; Thompson, Jerome. Substitutes not used: Margetson (gk), Boland, Loovens, Ndumbu-Nsungu.
Referee: C Penton (Sussex).
Booked: Cardiff City Scimeca, Thompson.
Man of the match: Mackay.