Youngster Todd Marshall kicked three goals and Ollie Wines racked up 35 possessions, as Port won to 14.10 (94) to 10.11(71) on Sunday.
Port kicked 10 goals to six in the second half to give them SCG wins in successive seasons.
The visitors trailed by eight and 14 at the first two breaks, but slammed on seven goals to four in the third, to carry a 15-point advantage into the final quarter.
Their lift in intensity pressured Sydney’s normally composed defenders into some uncharacteristic errors.
Captain Travis Boak started Port’s second half surge by kicking two goals in a minute.
Marshall also booted successive goals later in the quarter, as Port took control.
Long distance goals to Lance Franklin, who kicked a match-high four, and Dean Towers, got Sydney back to within four points early in the final quarter, but Port kicked the last three majors.
A 50-metre plus effort from Jared Polec after Oliver Florent gave away a 50 and majors from Sam Powell-Pepper and Riley Bonner secured the win.
The first half was a dour struggle, with Sydney failing to make the most of 21 extra inside 50s, but by the end each team had notched 52 entries.
Sydney lost midfielder Zak Jones before the game with a calf issue.
© AAP 2018
PORT ADELAIDE 1.2 4.4 11.7 14.10 (94)
SYDNEY 2.4 6.6 8.10 10.11 (71)
Goals: Port Adelaide: T Marshall 3 C Wingard 2 J Polec 2 T Boak 2 O Wines R Bonner R Gray S Motlop S Powell-Pepper.
Sydney: L Franklin 4 D Towers H Cunningham I Heeney L Parker T Papley W Hayward.
Umpires: Chris Donlon, Leigh Haussen, Andrew Stephens.
Official Crowd: 34,636 at SCG.