Both sides went into the match on nine points and were equal top of the league table. In a close first half, the visitors took the lead when Kevin Rutkiewicz turned a low cross past his own keeper. Darren Mackie had a couple of half chances for the home team, without failing to put Onstad under too much pressure.
With Darren Mackie and Calum Bett operating well on the flanks, the Dons started the second half well and drew level on the hour mark when Andy Dow crossed for French trialist Moussa Dagnogo to head home. The trialist then set up Aberdeen's second with a deft flick into the path of Rachid Belabed who made no mistake.
The third came on the stroke of full time when Dagnogo showed excellent composure after being put through by Belabed.