Jonny Hayes grabbed the goal which allowed interim Aberdeen manager Paul Sheerin to bow out on a high note.
The Pittodrie club's first away win of the year will also have delighted incoming boss Stephen Glass, who should emerge from quarantine to take charge of the Reds in next Sunday's Scottish Cup clash with Livingston.
Sheerin said a tactical change had allowed Hayes to take up a more offensive position in Saturday's 1-0 victory at St Johnstone.
And he was delighted with the impact made by half-time substitute Fraser Hornby, who provided a threat absent from Florian Kamberi's game in the first 45 minutes.
"It was a different shape that allowed the positional change for Jonny. We weren't trying to be overly clever with anything," said Sheerin. "We have to find ways of being better in forward areas.
"Maybe there is still more to come.
"Fraser was excellent. He had a wee niggle but managed to train on Friday. We weren't sure how much we would get out of him, but we pushed it. He gave us more presence at the top of the pitch.
"I thought he was really impressive. It would have been nice if he had topped it off with a goal.
"It was important to get off to a good start after the split, whether it was home or away."
With the Dons keen to close in on third-placed Hibernian and secure a European spot, Sheerin said Glass would be taking over a strong unit.
"Normally when you come into a club it's struggling in terms of league position but we are in a strong position to get into Europe like we have been in previous years," he said.
"We got the points with Matty Kennedy's good play and Jonny's goal.
"It was a vital three points for us to start the post-split fixtures."
Frustrated Saints manager Callum Davidson watched striker Chris Kane waste an early chance when his side were on top, while defender Shaun Rooney was denied by a post late in the contest.
"When you play a team of Aberdeen's quality you have to take your chances when they come along," said Davidson.
"If Kano had taken his chance in the first half it would have been us controlling the game.
"But I have to credit the players' attitude. We achieved top six at the last minute and won a cup this season so it would have been easy to take the foot off the gas."
