The home team went ahead on 15 minutes when the Frenchman took advantage of some slack defending to pick up the ball in the box and fire past Jamie Langfield.
At the other end, Michael McGovern was forced to keep out efforts from Adam Rooney and David Goodwillie.
Hamilton doubled their lead eight minutes into the second half when Andreu connected well with a Daniel Redmond cross to take his tally for the season to six.
Rooney and Niall McGinn missed chances to get Aberdeen back in it and the New Douglas Park crowd were sent home happy with a third goal in the closing stages.
Hamilton counter-attacked after breaking up an Aberdeen move and Ali Crawford found Mickael Antoine-Curier, who fired past Langfield in the 90th minute.
