A three-goal lead at three-quarter-time wasn't enough for St Pats as East Coast charged home to finish 7.9 (51) to 7.7 (49) victors.
In a match where 12 of the 14 majors were scored from one end, the two premiership hopefuls went toe-to-toe and the result was the opposite of the 2019 preliminary final.
St Pats got ahold of the scoring end first, leading by 10 points at quarter-time before the Swans led by two at the main break.
The Saints, led by recruit Jake King's three majors, pushed it out to 18 points going into the final quarter but were only able to get two behinds on the board in the final term as East Coast kicked 3.4.
Nick Child's return to footy picked up where he left off, booting four majors in the victory, as youthful pair Mitch Graham and Hamish Tate were named his side's best.
King's effort didn't go unrecognised but Liam Brown was named St Pats' strongest.
Selected by all coaches to go back-to-back this season, Lilydale got its premiership defence off to an impeccable start, defeating Perth by 122 points away from home.
A 10-goal second term set the platform for the dominant display as almost half the side booted a major in the 24-goal show.
Zach Cooke kicked seven off his own boot, with Billy Tuckerman (three), Thane Bardenhagen, Ruben Rothwell and Jimmy Storay in his first game back at his childhood club also joining in the party with multiple.
Matt McKinnon, who earlier in the week was described as one of the hardest workers coach Colin Lockhart has seen, was the Demons' best alongside Bardenhagen and Patty Sulzberger.
Will Haley was strong in his first game in black and white as Tarkyn Coppleman kicked two of Perth's five goals.
Old Scotch continued its winning form after their early-season match-up, defeating Old Launcestonians 12.10 (82) to 6.8 (44) in what some would describe as an upset.
Tall target George Walker, who was an integral part of the Thistles' NTFA Shield campaign, booted six and Charlie Eastoe three as they kept OLs at bay off the back of a six-goal opening term.
Dangerous goal-sneak Field Reeves kicked three for the Blues in defeat while the debuting Jay Schulz found the big sticks once.
Captain Jonty Swallow was best on ground followed by Matt Humphrey and Walker while Danny Hall, Mathew Murfet and George Mcadam were respected for OLs.
Bridport's trip to Evandale ended sweetly as the Seagulls triumphed 11.9 (75) to 3.10 (28).
Leading by only one point at the first break, the visitors kicked away, restricting the Eagles to just one more major for the day.
Matthew Taylor kicked four and Lachie Mason two in the latter's first game for the North-East side, while Cody Kerrison found the goals himself and was best on ground in the win.
Recruit Lachie Groves joined captain Jackson Davey in Evandale's best as Aidan Bullman, coach Sam Bouwman and Shane Cackett kicked goals.
Meander Valley got itself on the winners' list, defeating UTAS by 39 points away from home in a battle of last season's NTFA Shield competitors.
Keeping their opponents at reach all day, the Suns were led by Alex Wadley and Ben de Bomford's three majors apiece with Rory Lawrence and Wadley their best afield.
Chris Smith was the sole multiple scorer for the Lions, and was named their best, with Daniel Bluett and Will Geysing also impressing.