The success was their 24th consecutive win over Bunnings Warehouse Heartland opposition, their second Meads Cup win, after two Lochore Cup wins in earlier years.
Ten points scored by the home team during the sin-binning of first five-eighths Dane Whale turned the advantage to the home side, and they made the most of it running in three late tries to inflate the final score after having been behind for much of the game.
Whanganui led 22-17 at halftime, but were held scoreless while South Canterbury added 25 points before a 76th minute penalty try and a last minute try pulled the margin back a little.
But 14 Whanganui penalties conceded to only seven by the home team made life tougher, and South Canterbury goal-kicker and first five-eighths Sam Briggs landed 22 points.
It had taken Whanganui only 70 seconds to make their mark after halfback Lindsay Horrocks broke from the base of a ruck to slice through the defence with hooker Roman Tutauha on his shoulder to continue the move before feeding wing Alekesio Vakarorogo in for the opening try.
South Canterbury were undaunted, and while taking time to get maximum effect from lineouts from penalties in the Whanganui 22m area, they finally got reward when lock Anthony Amato built on a timely backline entry by fullback Liueli Simote to score after nine minutes.
An exhange of penalty goals preceded a lovely set-piece execution by the home side which saw centre Zac Saunders feed to Simote who beat a defender and ran in for South Canterbury's second try, after 21 minutes.
Twenty-nine minutes into the half, Vakarorogo made good ground and when he linked with Tutauha was supporting again. The ball moved out and wing Tyler Rogers-Holden broke two tackles and had the momentum to get over the line for a try.
Outstanding work by their big men lock Ben Whale, prop Gabrial Hakaraia and No8 Semi Vodosese created continuity play which created rare space, especially after the home defensive lost its shape, for second five-eighths Timoci Serawalu to break the line to score in a tackle three minutes out from the half.
South Canterbury came out for the second half and put Whanganui under pressure, and after a superb penalty kick to the corner by first five-eighths Sam Briggs, Whanganui lost Dane Whale to the sin-bin, but after attempting to run the ball all they got, initially, was three points from a penalty goal.
Whanganui looked to work themselves into position but, in attempting to add to their advantage, Robinson attempted a long pass only to see home wing Kalavini Leatigaga swoop on the intercept and race 70 metres to regain the lead for the defending champions. Moments later Briggs made it an eight-point lead with his third penalty goal.
Thirteen minutes from the end, flanker Nick Strachan pulled off a crucial turnover penalty in the shadow of the goalposts to allow another Briggs penalty goal.
Then, when a turnover occurred, as the result of a key play by centre Zac Saunders, it was replacement Salesi Savelio who pounced on a ball that squirted from the ruck to race 30m to score the try that sealed the game. He wasn't to be outdone when flanker Cam Russell ran a superb line to pick up a short pass and run to the posts on the tangent to score.
South Canterbury 47 (Anthony Amato, Liueli Simote, Kalavini Leatigaga, Salesi Savelio, Cam Russell tries; Sam Briggs 5 con, 4 pen) Whanganui 36 (Alekesio Vakarororgo 2, Tyler Rogers-Holden, Timoci Serawalu tries; Penalty try; Ethan Robinson 4 con, pen). HT: 17-22