The 18-year-old, recruited with the No.17 pick in last year's draft, kicked four in six minutes during the third quarter as the Dockers unexpectedly fought back into Saturday's match.
Down by 10 goals late in the second term, Fremantle pulled within four in the third before the Cats stomped on them in the last, running away to win by 78 points, 23.9 (147) to 10.9 (69).
The temperature went above 30 degrees and that probably influenced the low crowd of 25,372.
It was a day for the headbands, with Reid and star Geelong recruit Bailey Smith sporting the accessory.
There had been plenty of attention on Smith following his high-profile move from the Western Bulldogs and he did not disappoint in his Cats debut.
He capped an excellent game with his first goal for Geelong late in the last term.
Smith was a prime mover as Geelong opened up Fremantle in the first term, racking up 10 disposals and repeatedly driving the Cats into attack.
They kicked five goals to one in the first quarter and a blowout loomed as the domination continued for much of the second.
Dockers key forward Josh Treacy was on the end of a rare piece of fluent play out of the middle, midway through the second term, but his shot at goal was a shocker and it went out on the full.
Still, Fremantle were starting to win the ball out of the middle and Michael Frederick's goal after the halftime siren brought them to within 54 points.
Frederick then started the third term with his second goal as the Dockers rallied.
After losing centre clearances 6-4 in the first term, they won that statistic by a whopping 13-2 to three-quarter time.
Enter Reid, who had a set shot on goal at 22 points into the third term.
He outrageously played on and baulked around Gryan Miers, who himself had earlier kicked a contender for goal of the year, and slotted accurately on the run.
Reid quickly followed up with three more and the Dockers trailed by only 21 points at the last change.
But Geelong emphatically stopped the rot, kicking 10 goals to one in the last term for a convincing win.
Smith racked up a game-high 32 possessions and Jeremy Cameron kicked four goals, with the Cats having 13 goalkickers.
Reid had 13 possessions, while Dockers midfielder Jaeger O'Meara racked up 31 disposals.
Fremantle's Sam Switkowski left the game in the third term with a groin injury.
30°C