Portadown remain level on points with Premiership leaders Linfield after a comprehensive win at Seaview.
Matthew Tipton put them into a 17th-minute lead, strecthing to touch in Tim Mouncey's headed flick on.
Kevin Braniff made it 2-0 with a superb volley after Crues defender Gareth McKown did not cut out a clearance by Ports keeper David Miskelly.
Braniff made it 3-0 early in the second half, turning to shoot in after he had appeared handled the ball.
Ports defender Brian Gartland had a header clip the cross bar.
For Crusaders, Jordan Owens had a header clawed away by Miskelly.