An eighth-minute own goal from Aberdeen's Stevie Smith and midfielder Jamie Adams' second-half header proved the difference between the sides as the Dons failed to force Saints goalkeeper Peter Enckelman into any serious action.
The only bright spot for Aberdeen was the return of teenager Fraser Fyvie after a cruciate ligament injury, the midfielder coming off the bench midway through the second half.
Saints took a deserved lead after just eight minutes as Smith turned a cross beyond his own goalkeeper under pressure from Peter MacDonald. And they perhaps should have had a penalty when MacDonald seemed to be bundled to the ground by Zander Diamond four minutes later, but referee John MacKendrick was unmoved.
It was just 10 minutes from the interval when Sone Aluko blazed over with the Dons' first clear sight of goal, but the visitors' lead was doubled when Liam Craig swung in a corner from the right and Adams found space to bullet a header beyond the helpless Jamie Langfield.
The loudest cheer of the afternoon was reserved for Fyvie, who made his entrance after 66 minutes, replacing the ineffective Nick Blackman.
Source: PA
Source: PA