The Dons retained fourth place in the league through a goal in each half - Vernon finishing from a Jamie Langfield clearance in the first and Robson wrapping up the points shortly after the hour mark.
In difficult conditions, it was the hosts who had the first chance when Peter Pawlett forced Saints goalkeeper Peter Pawlett into action on the quarter-hour mark.
Vernon was wasteful in dragging wide of the post moments later but he didn't have to wait long for a chance to atone - nipping in between Kello and his marker to open the scoring.
The veteran striker should have doubled his tally before the break after good work from Willo Flood, and St Mirren came into the game on the counter-attack with Langfield saving well from Paul McGowan.
Aberdeen redoubled their efforts in the second half and made the game safe in the 65th minute. Robson's corner caught the wind and flew into the net beyond the reach of Kello, much to the delight of the home fans.
Vernon was inches away from a third soon after while at the other end, substitute Gary Harkins came closest to halving the deficit with 10 minutes left as St Mirren threw men forward in search of a riposte.
There was still time for one more moment of drama two minutes from the death - Vernon dummying a Jonny Hayes cross only for the ball to bounce back off the post - but the Dons ran out comfortable winners regardless.