One week on from the high of Irish Cup quarter-final success against Linfield at Shamrock Park, Glentoran arrived in town on Saturday.
Hopes of a second successive home scalp against city visitors ultimately ended in stalemate and a 1-1 draw.
Conditions proved problematic as strong winds and a difficult playing surface restricted the chances for flowing football.
Peter McMahon produced the home highlight by breaking the deadlock with a fine half-volley from inside the penalty area.
Glentoran levelled after the break for an outcome of honours even.
McMahon made his mark with the game’s first goal at the third attempt.
The early drama featured a penalty shout and claims for handball against Glentoran’s Niall Henderson following his block on the line off a Michael Gault header from Chris Casement’s corner-kick.
Appeals were dismissed by the match officials before McMahon cleared the crossbar with one effort then dragged another just wide of the target.
His third attempt produced the afternoon’s first goal as McMahon ghosted into the penalty area and smashed home a superb half-volley.
Glentoran’s response included a Stephen McAlorum drive over the bar then Curtis Allen header wide at the back post.
David Miskelly enjoyed a comfortable save off David Scullion’s snapshot but was unable to stop Jordan Stewart from hooking home the latter’s cross on 74 minutes.
Casement hit the post with a curling free-kick in the final moments.
PORTADOWN: David Miskelly, Chris Casement, Ross Redman, Keith O’Hara, Garry Breen, Peter McMahon, Sean Mackle, Tim Mouncey, Michael Gault, Gary Twigg, Robert Garrett. Subs: Billy Brennan, Mark McAllister (on for Mouncey, 82 mins), Ken Oman, Chris Ramsey, Shea Conaty.