The win made it two from two for the Dons since Derek McInnes announced his decision to stay on with the club, and they were impressive in Perth.
Although Saints boss Tommy Wright will be frustrated with the number of chances his side saw go begging in the first period, they were second best throughout against an Aberdeen side starting to reach top gear following an indifferent period.
Ryan Christie was particularly influential and grabbed a fortunate goal via a deflection after Adam Rooney and Kari Arnason had earned a two-goal lead at the break.
However despite their dominance, Aberdeen were lucky not to go behind after six minutes.
Stevie May, on his return to McDiarmid Park, was dispossessed in midfield before Stefan Scougall went scurrying down the wing and crossed for Murray Davidson who rushed his attempt from close range when he should have scored.
Aberdeen were ahead on the 20-minute mark however, as they worked the ball smartly inside the area from the left before Greg Stewart pulled back for Rooney - who hit a hat-trick the last time these teams met - to sweep first-time into the corner.
They continued to exert pressure, and should have been two goals up when the elusive Christie played a brilliant reverse through ball that split the Saints defence, only for May to smash against the bar when clean through.
They did not have to wait long for the second goal though.
May’s corner towards the near post was flicked up in the air and found Arnason at the far stick, and the Iceland international nodded in a simple second.
Steven MacLean should have pulled one back before the break after the ball dropped kindly to him following a Scougall corner, but Joe Lewis was out quickly to block before beating away a Michael O’Halloran effort to maintain their two-goal lead at the break.
A defensive lapse from Graham Cummins eight minutes after half-time almost saw the lead increased as he headed the ball back into the path of Rooney inside the area, but the striker blazed over under no pressure.
They did make it three just before the hour mark as David Wotherspoon was penalised for holding back Stewart, and Christie’s free-kick took a wicked deflection off the wall before finding the corner with Zander Clark wrong-footed.
The game fizzled out with Aberdeen dominating possession to leave Saints without a win at home since September 23.