They set a platform for cagey halfback Nick Annear to probe dangerously around the fringes, while his fellow Christchurch import Cameron Bailey carved off some big metres at centre with his boot.
The pressure even led to a first for Wanganui in taking the two-point penalty option for first-five Steve Crosbie, who was brave in taking on the line all match but needs time to develop further continuity with his outside runners.
In the end, Wanganui kept faith in their skill of ball-in-hand, with returning No8 Malakai Volau having an outstanding match, including scoring what proved the winning try with six minutes left when his planned move of a reverse inside pass to reserve Jamie Hughes set Volau up to score by the posts.
Wanganui seemed safe at 32-22, but completely fluffed the kickoff as huge South Canterbury reserve forward Taione Ratu swooped through to snatch the loose ball and go under the bar.
Ratu then nearly set up the matchwinner as his great offload saw winger Maxx Morris breaking clear, but fullback Ace Malo lowered him in a great tackle and then the visitors pass cannoned into a support player's head.
Wanganui relieved the pressure with a penalty kick from the scrum and then controlled the ball near halfway for the last 90 seconds before booting out.
Volau, prop Tietie Tuimauga and sore lock Gavin Thornbury spent the entire game grappling in the furnace with the South Canterbury pack and emerged with their noses just in front.
"Hat off to a good side, that first half they put on a lot of pressure. Whether it was just our errors and penalties," said captain Peter Rowe.
"We needed today. It will just pull us into training and bring a bit more intensity."
Coach Jason Caskey agreed, noting the step up in opposition led to his team reverting to some bad habits of overextending, which nearing halftime had them trying to overcome a 9-2 penalty count.
Attacking in the halfway to 22m zone suddenly had them jogging back to face penalty lineouts or scrums.
"They got a bonus 30m on us [each time]. They're a good team and they've got some big boys too," said Caskey.
"That's a good wakeup. Bring it back to what Heartland's all about."
The coach may also spend some training time on kickoff retention for the players not named Thornbury, as the Ratu try nearly led to disaster.
"We could have shut them out, taken the five [competition points] and given them nothing.
"Then suddenly in one minute you're back down your end, defending for your life. It's a coach killer, that one."
Still leaving town with two competition points, the Cantabrians remain a big threat for the Meads Cup playoffs again this year.
Both Kuruyabaki and Waitokia were asked early questions as Wanganui coughed up the ball on their rare chances to attack, and South Canterbury worked smartly into position.
Wanganui's pack were tested for the first time since the Waikato match as their scrum was screwed around and from the penalty lineout, the visitors rumbled to the goal line and then fed flanker Nick Strachan to force his way over.
Logavatu created havoc with a barnstorming run up the middle and while Wanganui kept giving away penalties, their tackling held firm.
Kuruyabaki redeemed as his team got field position from a penalty and Malo spotted the half gap - feeding his second-five who powered through and although dragged down short of the line, popped the ball to Volau to give Wanganui an 8-6 lead against the run of play.
South Canterbury rapidly shook it off and pounded the home team's line, with Annear just sniffing out the gaps, and after Wanganui stopped them cold three times, the door was slightly ajar and the little halfback was through for 14-8 after 31 minutes.
But you can't plan defence for helter-skelter and just like last year in the final, Wanganui concocted a wild try for winger Samu Kubunavanua, still not running full gallop on his ankle, in the 49th minute.
Kuruyabaki slipped gathering a clearing kick but popped up and ran right through his pursuers, finding Thornbury who sent the ball to a motoring Tuimauga.
His hail mary pass back inside somehow cleared the cover defence and found Wanganui hands, with Kubunavanua getting the ball down in the corner.
Two minutes later, fresh reserve Bryn Hudson smashed his way up the centre and halfback Lindsay Horrocks finally found a chink in South Canterbury's armour, dashing through and delaying his pass a fraction to give his big mate Thornbury an open tryline.
But the visitors hit back immediately as Wanganui missed the kickoff and shortly after the front row got pushed up in a scrum, with South Canterbury getting the penalty and driving in from alternating directions to get prop Conor McCormack over the line for 22-22.
With Rowe subbed, reserve Cole Baldwin took over the captaincy and made the call to take a 22m penalty in front for Wanganui's first two-pointer and some breathing space, and from then on they went back to attempting tries.
South Canterbury were holding right on their line, until a 15m scrum where Wanganui rolled the dice on the Volau reverse flick pass and it worked a treat with Hughes dashing through and then putting Volau over by the posts.
The match now seemed safe, but Ratu's try 20 seconds later set up a heart-stopping final five minutes.
Wanganui 32 (Malakai Volau 2, Samu Kubunavanua, Gavin Thornbury tries; Steve Crosbie pen, 3 con) bt South Canterbury 30 (Nick Stachan, Nick Annear, Conor McCormack, Taione Ratu tries; Zac Southen 3 con). HT: 14-8 South Canterbury.