After the Saints had kicked the first three goals of the game, live-wire Hayden Ballantyne sparked a Freo revival with two excellent goals.
But the Saints steadied late in the second quarter to take an advantage into the main break.
Michael Barlow leads the possession count with 13 disposals and a goal, while Paul Duffield has also been prominent with 11 disposals.
Fremantle 4.5 (29) trails St Kilda 8.6 (54)
