A second-half double from Scott Vernon, both coming from Chris Maguire crosses, was enough to down the Buddies, who are now four points behind the Dons.
After a forgettable first 45 minutes, the Dons broke the deadlock five minutes into the second half when Vernon chested home and the former Colchester United striker headed in a second after 67 minutes to put the game beyond doubt.
New signing Rob Milsom was handed his Aberdeen debut in place of suspended skipper Paul Hartley but fellow new recruit Nick Blackman, who has joined the Dons on loan from Blackburn, missed out on making his Pittodrie bow due to a virus.
Aberdeen's only other change from their 6-0 Scottish Cup triumph over East Fife saw Josh Magennis replace the absent Sone Aluko.
The Buddies were forced to make three changes with Michael Higdon and Marc McAusland injured and Paddy Cregg missing out through suspension. Irishman David van Zanten, former Don Lee Mair and former Falkirk midfielder Sean Lynch came in as replacements.
Aberdeen's top scorer Vernon, who had recovered from flu to start the match, almost released his strike partner Maguire in the opening minutes but Saints captain John Potter was alert to the danger and made a perfectly-timed tackle on the young striker.
The visitors carved out the first real opening of the game when on-loan Celtic man Paul McGowan picked out Craig Dargo and the former Inverness striker drifted past Rory McArdle before unleashing a low shot that went just wide of the target.
At the other end, Mair was in the right place to block Maguire's powerful volley before defender Andrew Considine headed over from the resulting corner as the home side pressed for the opener.
Aberdeen youngster Ryan Jack had made a lively start to the match and should have done better after 28 minutes when he volleyed the ball woefully off target from a promising position.
Milsom almost made a dream start to his Aberdeen career when he showed a terrific turn of pace to glide past Jim Goodwin before drilling a low shot at goal that drew a fine save from Paul Gallacher.
The home side were forced to make a change five minutes before the break when David McNamee limped off and was replaced by Nikola Vujadinovic.
On the stroke of half-time Milsom, the former Fulham player, went close again when he dragged a left-foot shot inches wide of the target.
Aberdeen opened the scoring five minutes into the second half when Maguire darted past van Zanten on the left wing before curling an inviting cross into the penalty area that Vernon chested home from two yards out for his 11th goal of the season.
The impressive Jack almost doubled the advantage when he slalomed his way past two Saints defenders before firing a shot over the bar.
Aberdeen's forward pair linked up again to give the home side their second after 67 minutes with Maguire producing another tantalising delivery which was nodded home by Vernon at the back post.
The home side almost gifted the Saints a way back into the game when Vujadinovic's back pass was intercepted by Buddies substitute Paul McQuade but the midfielder's chip drifted just over the bar.
In the closing stages Maguire curled a free kick wide from 25 yards before St Mirren substitute Aaron Mooy blasted over from the edge of the area to cap off a day to forget for the Paisley side.