The Kangaroos started well and never dropped their heads but the Saints always had the match in their keeping after halftime, going on to win 15.13 (103) to 10.5 (65).
Young gun Darcy Wilson put in a compelling bid for the round-eight Rising Star nomination, picking up 21 disposals and booting three goals.
Young gun Darcy Wilson had a breakout game in the win over North Melbourne. (Joel Carrett/AAP PHOTOS)
The bottom-placed Kangaroos made a bright start to the game, booting three successive goals midway through the opening term to gain an early 12-point advantage.
The third of those goals came when St Kilda defender Webster's kick across goal was intercepted by North Melbourne youngster Tom Powell.
Webster predictably earned the opprobrium of the Kangaroos fans, having been suspended for seven weeks for a late, high shot on North co-captain Jy Simpkin in a pre-season game.
Simpkin was the first Kangaroo to get in Webster's face on Saturday after the error.
The Saints then wrested control of the game, kicking six successive goals either side of the quarter-time break, a run finally broken late in the second term by Kangaroos forward Cam Zurhaar.
Small forward Paul Curtis kicked the first goal of the third term to trim the margin to 21 points, but the Kangaroos never got closer than that as the likes of Jack Sinclair, Nasiah Wanganeen-Milera and and Marcus Windhager kept the Saints in control.
Playing his first game since breaking his collarbone in round two, former Kangaroo Wood was among St Kilda's best players.
Former Kangaroo Mason Wood (left) made a successful return from injury for the Saints. (Joel Carrett/AAP PHOTOS)
North Melbourne's better players included young guns Colby McKercher, George Wardlaw and Harry Sheezel.
Fullback Aidan Corr comprehensively won his battle with St Kilda spearhead Max King.
The Saints improved their win-loss record to 3-5 ahead of a round-nine clash against Hawthorn in Launceston.
The Roos' next match is against Gold Coast in Darwin.