Other than his yellow card, Horrocks again suitably inspired his team with directional impetus and hustling defence, while captain Peter Rowe got through a lot of work around the fringes, especially when Wairarapa Bush held the ascendancy.
Reserve centre Cameron Crowley's introduction into the match proved decisive as the veteran showed all the timeless skills with beautiful stepping and determined angled runs to score two tries - the first of which was a great dash from near halfway to break the 22-22 deadlock.
Also scoring twice, young fullback Te Rangatira Waitokia continues to grow into his jersey with some great scything bursts and try-saving tackles, particularly the 'grass cutter' to bring down big lock Andrew McLean, who had run through three defenders before Waitokia took his legs out.
Cole Baldwin put his hand up for getting the permanent starting hooker's spot with a typically aggressive performance in the first half .
However, a couple of players limped out of the physical match, to go along with those already on the injured list, so coach Jason Caskey has to keep his plans fluid regarding who will make up his core squad of 22 to prepare for West Coast this Saturday.
"We're a bit of a hospital ward at the moment.
"We were a bit flat today, to be fair.
"Next week that won't be a problem, we won't let it be.
"We're playing for 80 minutes and not folding up. We just don't want to let them come back, and to have discipline."
Captain Peter Rowe said being back in a scrappy kind of game had "served that purpose".
"I've been thinking the last couple of weeks, it hasn't been like Heartland footy.
"That's the positive - it's given us a lot more to work on."
He was confident the side will adjust to the new laws around the breakdown so that they can still impose their will in matches.
"To be fair, Wairarapa Bush did it well.
"That first guy [over the ball] seemed to be making it very hard - you've got to come in with the right motion."
Wanganui attacked from kickoff but nearly gave away an intercept try to centre Cameron Hayton until Waitoka caught him.
Returning centre Craig Clare made his presence felt with a bone-rattler on Wairarapa Bush fullback Glen Walters, which paid dividends shortly afterwards as winger Michael Nabuliwaqa was freed up down the far side and brushed aside the weakened Walters for Wanganui's first six-point try.
Wairarapa Bush's veteran first-five Tim Priest was kicking well for territory, yet Wanganui tried to keep the roll on and eventually got a penalty lineout close to the line, with lock Gavin Thornbury feeding Baldwin to smash his way over.
Waitokia was looking threatening and seven minutes before halftime, Horrocks made the gap from a lineout and the ball eventually spread back towards the far corner, where Clare drew two defenders to him to put the speedy fullback away.
However, Wanganui took their eye off the prize as McLean smashed through until his legs met Waitokia's shoulders, and then winger Nick Olson hit a gap and Horrocks was binned for a scragging high tackle on second-five Andy Humberstone.
Wairarapa Bush attacked the line and despite Rowe stopping his opposite Eddie Cranston twice, the crack appeared and hooker Richard Puddy dived through for 22-8.
Bringing on half their larger bench at the resumption, Wairarapa Bush kept the momentum going with halfback John Ika moving out wide and stepping up big time - first scoring from an inside pass at a tryline ruck, then making a midfield dash with the ball going wide for Humberston to dive over in the far corner.
Horrocks made up for his transgression with aggressive defence and marshalling the backline, and finally the ball got wide to an open Crowley who pivoted off both feet to round his tacklers and score in the corner.
Wanganui got another scrum near the line and Waitokia showed great strength to shrug off a collaring tackle and be driven over by two team mates for 34-22.
Crowley emulated that effort with three minutes left, as he shrugged off one defender and scooted low to cross for the matchwinner.
Wanganui 40 (Te Rangatira Waitokia 2, Cameron Crowley 2, Michael Nabuliwaqa, Cole Baldwin tries; Dane Whale 2 con) bt Wairarapa Bush 22 (Richard Puddy, John Ika, Andy Humberstone tries; Tim Priest 2 con). HT: 22-8.