Power captain Travis Boak (27 disposals) and Hamish Hartlett (26 touches) were influential in a victory which all but kills off the Lions' chances of making the finals.
The Lions were inspired by dynamic midfield duo Jack Redden and Tom Rockliff, who collected a game-high 28 possessions, while Dayne Zorko and captain Jonathan Brown booted two goals each.
But the Lions were unable to claw their way back from a four-point deficit at three-quarter time.
Port's Chad Wingard ended a remarkable stalemate in the last term - kicking a goal after nearly 16 scoreless minutes to give the Power breathing space.
Port held sway early and led by 3.4 to 1.4 when Justin Westhoff kicked a goal after the quarter-time siren.
But the Lions' prolific ball-winner Daniel Rich led a rapid response, providing three goal assists as the Lions took a three-point lead 15 minutes into the second term.
Port then launched a challenge of its own as impressive youngster Ollie Wines and John Butcher scored majors within two minutes of each other for the Power to lead 5.9 to 4.5 at half-time.
The Lions, with Zorko scoring twice, booted five goals to three to creep within four points at the last change.
But despite kicking with a stiff breeze in the final term, the Lions were held goalless - registering just two points as Port relentlessly defended until Wingard's goal broke the deadlock.
Port meet home-town rival Adelaide next Sunday while the Lions host St Kilda on Saturday night.
Lion Brent Moloney is swamped by Port Adelaide players on Sunday. Photo: AFL Media.