The lineout was again in trouble as Mid Canterbury lifted their inspirational flanker captain Jon Dampney into the path of hooker Cole Baldwin's throws.
Outstanding Mid Canterbury first-five Murray Williams was given three penalty chances right in front and the Auckland import was not about to miss, and then he charged through a gap at the line to dot down under the posts for 16-6 in the 36th minute.
But Wanganui clicked into gear with their speed and athleticism, as winger Michael Nabuliwaqe somehow snuck through on the 40m line and flirted with the touchline while he slipped three tacklers to score.
Climbing after half-time with fullback Trinity Spooner-Neera chiming in at the right moments and being accurate with his kicking, the Wanganui pack took Mid Canterbury on up front with their signature pick-and-go and camped down in their half for the third quarter.
Williams had pulled his hamstring in scoring the try to leave his South Island team rudderless while struggling with clearing kicks into the slight wind.
However, leading by 12 and hunting a four-try bonus point, it all went wrong for the home side as they could not get away from the glare of Wairarapa-Bush referee Alistair Payne.
Having survived the sinbinning of lock Sam Madams right on half-time for retaliation punching after a big brawl, Wanganui were then deprived of Latu in the 68th minute for a professional foul, which followed Payne handing out repeated team warnings for obstruction or going off their feet at the breakdown.
In the end, a 16-5 penalty count against them and playing 20 minutes with 14 men proved too much of a hurdle.
Prior to Latu's marching orders, Wanganui had gambled by bringing on reserve hooker Roman Tutauha for prop Viki Tofa and moving Baldwin to the open side, figuring that despite his lack of game time at prop 75 games experience was still better than throwing teenager Tawhio Gupwell to the lions.
So with Latu gone and standout flanker Fraser Hammond therefore having to make way for the scrum specialist Gupwell, Wanganui were now camped on their line with two hookers and a rookie prop up front, and the tide eventually told when No8 Seta Koroitamana ran off the back and put Caucau over untouched following sustained pressure for 28-23.
It still appeared Wanganui would be safe as they attacked from the kickoff and secured possession, with returning reserve loose forward Bryn Hudson making some great runs.
But the pressure was on Hekenui and he would rue two crucial moments - the first a forward pass to Spooner-Neera on halfway letting Mid Canterbury surge back on to attack.
Wanganui finally turned the ball over on their 15m line from a Mid Canterbury fumble, which the scoreboard timer nearly at zero, although Payne told captain Peter Rowe there was 90 seconds remaining.
Reserve halfback William Short struggled to collect the scrum ball and after getting the pass plus two tacklers at once, Hekenui could not kick clear and instead grubbered behind himself, which put the lineout right on Wanganui's 5m.
Knowing the next whistle was the last, Mid Canterbury showed all the composure of a champion team and poured phase after phase at Wanganui, right on their tryline, as Rowe and the rest of the forwards kept up the same hard tackling they had all game, but without any free ground behind them.
After three minutes of non-stop pounding, the cracks had formed and Caucau twisted through two tacklers to score right beside the posts, with the conversion academic for reserve first-five Ewan Scott.
Coach Jason Caskey, who did not bring back Madams after his indiscretion, will have to address the team's nature to get frustrated when things are not working for them, because an 11 penalty deficit against Heartland's best team is too much for any side to overcome.
"We missed that try down there, and they said penalty against [Hudson, for double movement]. That would have been game over," said Caskey.
"We did so much good work in between."
The other issue is the early errors because while Horrocks, Spooner-Neera et al are very good instinct players, there is no value in throwing risky passes in traffic or at player's boot laces just because a break may be on.
"We said at halftime, we were living off bugger all ball," said Caskey. "They're just pushing the pass with the out-the-back, when we should have just held it."
Rowe knew the side could still be their own worst enemy.
"There were the things we could control that cost us. It sucks to lose but impressed with the lift."
Likewise, the debilitating penalty counts needed to be addressed, he said.
"It's still a concern. We've got to learn to take the ref out of the game."