Portadown will face a three-goal deficit in their Setanta Cup quarter-final second leg after Monday's defeat by Sligo.
Rovers took the lead on 21 minutes when John Dillon followed up after keeper David Miskelly had saved Matthew Blinkhorn's header.
Portadown had the ball in the net but Richard Lecky was judged to have fouled Gavin Peers.
Goals from John Russell and Rafael Cretaro left the Ports well beaten.
Russell tapped in from close-range on the hour mark after Aaron Green had pulled the ball back.
Then substitute Cretaro got his first goal since returning to Sligo near the end after Russell had set up the chance.
Ports manager Ronnie McFall rested key players like Kevin Braniff and Matthew Tipton as they play Lisburn Distillery in the final of the Co-operative Insurance Cup on Saturday.