Then came the penalty, and United went further ahead in the 28th, through Malcolm Marfell, to lead 3-1 at halftime.
Josh Adams scored from 18 metres to make it 4-1, and Dane Thompson rose to power home Marfell's left-wing corner for 5-1.
Wainui got one back, for 5-2, before Josh Adams brought up his hat-trick, taking a throw-in from Corey Boocock on the right, turning and volleying the ball into the far corner with his left foot.
Blair scored his second goal of the game when he followed up and hit a rebound from the keeper into the goal.
With the sending-off, 1st Class Decorators Wainui Sharks lost not only their keeper, but also the outfield services of Korbi Schallinger, who went from centreback into goal.
Strikers Jack Tobin, Jake Theron and Dan Torrie (up from leftback) scored for Sharks. Their man of the match was central midfielder Shane Hooks, with Max Logan and Connor Findlay also outstanding in the engine-room.
Defender Andrew McBride did well until his hamstring strain forced him off.
For United, Mal Scammell and Kieran Higham combined well at the back, teenage schoolboy rep Kaden Manderson put in a good shift at leftback, and midfielder Baxter Mackay — in his second game for United — showed his sporting talents extend beyond cricket and rugby.
Thistle Youth and Tatapouri Bohemians drew 2-2 at Childers Road Reserve. The Bohs went 1-0 up through midfielder Caleb Craig in the 14th minute, Thistle equalised on halftime through Daniel Robinson and then went ahead in the 55th through Oska Smith. Bohs midfielder Steve White tied it up with a penalty, for a push, in the 83rd.
Thistle coach Matt Harvey said their man of the match was midfielder Max Kume, who featured in much of the play.
Centrebacks Brad Hill and Daniel Walters were solid, and skipper Shannon Dowsing had a “stormer” at rightback. Fletcher Stewart-Hill and Phill Gloistein shared the defensive midfield duties.
For the Bohs, leftback Luke Fisher, right-winger Ron Martens, Craig and White were outstanding.
Strikers Stu Cranswick (two), Aubrey Yates and Damon Husband scored the goals for HES United Firsts in their 4-0 victory over Sunshine Brewing Wainui Salty Dogs at Harry Barker Reserve.
United's best were Cranswick, holding midfielders Ben Hansen and, in an unfamiliar role, Matt McFatter, central defenders Kyle McVey and Jonathan Purcell, and keeper Andy McIntosh.
Best for Wainui were midfielders Rick Kitto and Simon Blaker, leftback Hone Pewhairangi, rightback Barry McCarthy, and strikers Marcel and Henri Campbell.