Kavanagh, who scored twice in 10 games last season after arriving from Bradford in January, struck twice in the space of 15 minutes to earn the Latics an opening-day victory.
The deadlock was broken on the hour when the Valiants were caught out by a quickly taken Ollie Norburn free-kick as Republic of Ireland under-21 international Kavanagh raced clear to slot a shot low past goalkeeper Jackson Smith.
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And it got even better for Kavanagh when he added a second goal in the 75th minute.
Mike Fondop's acrobatic overhead kick from Keenan Appiah-Forson's cross was flying wide but found Kavanagh who slotted home a low shot.
Oldham goalkeeper Matt Hudson, who last season recorded a club record with 19 clean sheets, started this campaign with another shutout.
Vale, with pop star Robbie Williams as their new shirt sponsor, rarely threatened Hudson's goal, with their best chance a 35-yard drive from Jordan Lawrence-Gabriel which whistled past the upright.
