Linfield's march to a 57th Gibson Cup continued under the lights at Seaview on Friday night.
Blues keeper David Walsh was called into action early on in the first half, denying Harry Franklin with a smart save down to his right. Callacher then came closest to breaking the deadlock late in the second half, but his header struck the crossbar and went behind.
Linfield had the ball in the net on the stroke of half-time but Fitzpatrick was deemed to have been in an offside position as he interfered with play right on the goal line.
The Blues almost found the first goal of the evening early in the second half, as Fitzpatrick couldn't direct Ben Hall's flick-on on target, despite being just a yard from goal.
Linfield exerted control in the second half, and were rewarded as Orr rose highest to meet Kyle McClean's cross to break the deadlock, with his looping header beating Jonny Tuffey.
Fitzpatrick made it 2-0 when his right-foot strike from just inside the box sneaked in at the nearpost.