In the 15th minute Patrick O'Keefe scored the first of his two goals after collecting a beautiful through ball and coolly slotting the goal from 20 metres past United keeper Scott Basalaj on the angle.
Josh Margetts had the chance to restore United's lead after 33 minutes, only for his thunderous shot from 10 metres to slam off the crossbar.
O'Keefe evened the scores on 40 minutes, again given too much room by United's leftside defence, and scoring from the edge of the box.
The second half started in the same manner as the first spell finished with Lower Hutt taking full advantage of the space given by the United defence, and the lively Malcolm Finney blasting a shot past keeper Scott Basalaj to make the score 3-2.
That seemed to be the spur United needed and they dominated the rest of the match.
After 55 minutes Viera put a header just over the goal.
He had his reward six minutes later with a diving header from a lovely Nathan Cooksley cross finding the back of the net.
United continued to press for the winning goal but stout Lower Hutt defence denied them until the 76th minute when Mason-Smith completed his hat trick putting away the goal after a jinking run by Cory Chettleburgh to the byline.
Mason-Smith made it goal number four on 83 minutes after the Lower Hutt defence failed to deal with a loose ball.
For United, strikers Mason-Smith and Viera always looked threatening, while Chettleburgh and Cooksley caused the opposition defence problems with their searching runs, especially in the second half.
Seventeen-year-old Liam Hare again impressed in a 20-minute cameo, with some slick passing and forcing the corner that led to the fifth goal.
In Capital Division 2, Douglas Villa let a 3-1 lead slip to hand Lower Hutt City their first win of the season, 4-3.
Property Law Service Masterton had a 3-1 victory over Island Bay United and moved to fifth place on goal difference in Capital 4.
The Wairarapa United seconds game in Capital 3 was postponed.
