Wainui scored their goal about 60 minutes in, Matais Casablanca cracking in a free-kick from 25 metres.
United midfielder Dane Thompson completed the scoring in the 85th minute.
He hit a curling chip from the left corner of the penalty area with his right foot (his wrong 'un) and it dipped and swerved into the top far corner.
Adams changed things at halftime. Although his side were 4-0 up, he wanted to stop the Wainui frontrunners from receiving the ball in the space between United's defence and midfield. And he wanted to give his subs a run.
Fullbacks Jonny Curle (on the left) and Kaden Manderson were injured, so Adams brought on Corey Boocock for Manderson, shifted Marfell to leftback and brought on James Bristow as a defensive midfielder to disrupt the supply to the Wainui frontrunners.
United had Corey Adams and Thompson in front of Bristow, and wide frontrunners Jacob Adams on the left and Baxter Mackay on the right to drop back when needed.
Josh Adams had formed a two-pronged strike force with Mackay in the first half, when Jacob Adams had been at right midfield in a 4-4-2 formation.
They played 4-3-3 in the second half, Josh Blair taking over the central striking role from Josh Adams.
It was a solid outing for United. Kieran Higham and Mal Scammell in the heart of the defence, Corey Adams, Marfell and Thompson in midfield, and Jacob Adams and Mackay up front all did their jobs and more.
Wainui coach Blake Mulrooney said his side played “quite well” but if they were caught overplaying their build-up, United had the speed to make them pay, especially on the small pitch.
Left midfielder Daniel Torrie was their man of the match, and fellow midfielders Connor Findlay and Max Logan also put in good shifts.
Rightback Greg Judd defended well.He and Henri Campbell have been helping the Sharks get through some short-handed weeks, and on Saturday they were joined by Sunshine Brewing Wainui Salty Dogs teammates who pitched in as subs. Mulrooney said it was much appreciated.
Thistle Youth coach Matt Harvey was also appreciative of the help he received from Tim Smith and Dan Murphy from third division team Tumu Thistle, and from his co-coach of the under-15 rep side, Matt Adams, of Thistle Vintage.
Of the regulars, right midfielder Luk Stoltz had a stormer, in both defence and attack.
Opponents HES United Firsts had too much power, though, and won 8-0.