Monfries kicked seven goals in his best individual performance since coming to Alberton last summer.
It followed on from his strong effort against Adelaide in last Sunday's Balfours Showdown.
But Simonds Stadium remained a fortress for its tenant as the Cats opened up an early lead and never looked back.
Port is one of only two teams (the other being Sydney) to defeat Geelong at Simonds Stadium in the past 43 matches at the ground - that win coming back in 2007.
Geelong opened the game with five goals to Port's one and extended that to a comfortable 51-point lead at the half-time break.
The Cats' ball usage and disposal efficiency was critical to its first-half dominance, while its excellent set-shot accuracy ensured the Power was held at arm's length throughout the day.
Port was in for the fight and was effective enough at stoppages to create opportunities inside 50.
But Geelong's pressure around the ball proved the difference at effecting turnovers and punishing Port on the scoreboard.
Things looked dire for the visitors when the Cats extended its lead to 58 points at three-quarter-time.
But as it has done throughout the season, a fast-finishing Port Adelaide ran out the match to fall by just four goals at the close of play.
FINAL SCORES
GEELONG 6.4 12.7 19.9 20.9 (129)
But as it has done throughout the season, a fast-finishing Port Adelaide ran out the match to fall by just four goals at the close of play.
FINAL SCORES
GEELONG 6.4 12.7 19.9 20.9 (129)
PORT ADELAIDE 1.3 4.4 10.5 16.8 (104)
GOALS
Geelong: Selwood 4, Taylor 3, Podsiadly 2, Christensen 2, Motlop 2, Bartel, Hawkins, Varcoe, Guthrie, Caddy, Kelly, Walker,
Port Adelaide: Monfries 7, Schulz 2, Boak, Gray, Ebert, Lobbe, Colquhoun, Wingard, Moore
INJURIES
Geelong: Duncan (concussion)
Port Adelaide: Nil
SUBSTITUTES
Geelong: Jesse Stringer replaced Mitch Duncan (concussion) in the first quarter
Port Adelaide: Kane Mitchell replaced John Butcher in the third quarter
Reports: Nil
Umpires: Rosebury, Ryan, McInerney
Official crowd: 24,784 at Simonds Stadium
