The Power prevailed 16.11 (107) to 9.13 (67) in Sunday's Adelaide Oval twilight fixture to join Hawthorn and the Cats at the top of the table.
The trio all have five wins and a loss after Port dismantled the Cats in grand style before a raucous home crowd of 47,007 spectators.
The Power were inspired by the ball-winning feats of captain Travis Boak (32 disposals, two goals), vice-captain Brad Ebert (28 possessions) and Kane Cornes (33 touches), while forward Chad Wingard kicked three goals.
Port's livewire forward Robbie Gray capped his outstanding game with two goals, a return matched by teammates Hamish Hartlett, Matt White and ruckman Matthew Lobbe.
The Cats were well-served by Matthew Stokes (28 disposals), Steve Johnson (25 touches) and Mitch Duncan (27 possessions) but butchered a host of scoring chances with errant goalkicking.
Key forward Tom Hawkins slotted three goals from limited opportunities and Josh Walker booted two but the Cats paid the price for wasteful goalkicking, particularly in the second quarter.
In a freewheeling game, Geelong held a two-point advantage after both sides kicked four goals in the opening quarter.
Both teams then had five scoring shots in the second term: the Power logged 4.1 while Geelong returned just five points.
Geelong's inefficiency helped Port create a three-goal break at half-time - a margin the rampant hosts doubled in the initial six minutes of the third term when the influential Gray slotted his second.
The Cats briefly rallied but could only get within four goals before Port kicked away again, taking a defining 38-point buffer into the last quarter.
Port's reigning club champion Wingard then capped a stunning Port victory with two quick goals in the last quarter.
PORT ADELAIDE 4.2 8.3 13.6 16.11 (107)
GEELONG 4.4 4.9 6.10 9.13 (67)
GOALS
Port Adelaide: Wingard 3, White, Boak, R.Gray, Hartlett, Lobbe 2, Young, Schulz, S.Gray
Geelong: Hawkins 3, Walker 2, Johnson, Horlin-Smith, Blicavs, Bartel
BEST
Port Adelaide: Boak, Ebert, Lobbe, Cornes, Gray, Hartlett
Geelong: Johnson, Duncan, Stokes, Kelly, Bartel, Guthrie
INJURIES
Port Adelaide: Nil
Geelong: Nil
SUBSTITUTES
Port Adelaide: Sam Gray replaced by Jarman Impey at three-quarter time
Geelong: Josh Walker replaced by Taylor Hunt in the second quarter
Reports: Nil
Umpires: Fleer, Meredith, Mollison
Official crowd: 47,007 at Adelaide Oval
