The first fell to Raymond How in the 15th minute after a stinging shot from skipper Sam O'Regan deflected off the post following a corner.
The lead doubled in the 31st minute thanks to Andrew Cooper's left foot.
The third just before the break put the game away and summed up the visitors' day.
A Waiuku defender's attempted clearance was, in fact, a perfectly placed volley into his own net. It sucked all the life out of the visitors, who barely threatened all day.
McNab notched another in the 50th minute with a clinical set-piece header at the back post, triggering a regression in the quality of the match.
Jerahl Hughes left with a return of a hamstring niggle before Cooper, and O'Regan were replaced with an eye to Monday's home match against a Papakura FC side that sat fourth coming into the weekend.
Tom Livesey finished off the rout with a popular strike in the 90th minute.
Another defensive blunder left Livesey one on one with Waiuku goalie Justin Baldwin.
The first-time right-footed finish was perfectly placed - the 12th City goal of the season against just three.
The side needs a top-three finish to win promotion, something coach Duncan Lowry knows is sorely needed.
Today's matches kick-off at 2.30pm.
Tauranga City United 5 (Raymond How 15', Andrew Cooper 31', own goal 45', Jack McNab 50', Tom Livesey 90) Waiuku AFC 0.