Portadown survived second-half pressure to leave The Oval with a league point from the Irish Cup final dress rehearsal.
The scoreless draw was played out in strong winds that restricted the chance for passing football - despite high stakes with both sides pushing for European qualification.
Billy Brennan proved in the correct position early on to collect Jordan Stewart’s speculative shot from distance.
Portadown then enjoyed a short spell on top, with Shea Conaty unable to gain a clean connection on Sean Mackle’s looping cross after a sweeping pass out wide by Peter McMahon.
Jordan Lyttle - so impressive in the midweek win against Crusaders - replaced the injured Ken Oman with six minutes on the clock and produced another assured display.
He came close to finding the net but his back-post header under pressure drifted wide after good work by McMahon.
Robert Garrett and Gary Twigg combined to create space around the edge of the penalty area but the midfielder dragged his shot wide of the target.
Lyttle was on hand with a sliding block to clear the danger a few yards in front of the exposed net off Danny McKee’s shot.
Portadown squandered a golden opportunity to break the deadlock on 35 minutes when McMahon’s clever turn and cross was controlled by Twigg but Elliott Morris blocked the shot with his legs.
Twigg collected a pass from deep by Darren Murray early in the second half. However, with two defenders blocking his path to goal, the striker opted for a shot from distance that cleared the bar.
Glentoran had the upper hand after the break but Portadown managed to protect the clean sheet.
Brennan pulled off an acrobatic and inventive save to deny McKee with a crucial forearm touch that diverted away the close-range flick.
Moments later he raced out with a brave block to frustrate David Scullion.
Kym Nelson flashed an angled long-range drive past the post as Glentoran pushed hard.
Another superb chance arrived for Twigg at the back post but he hit the upright off Chris Casement’s teasing low cross, following a well-worked passing move involving McMahon and Garrett.
GLENTORAN: Elliott Morris, Willie Garrett, David Scullion, Steven McCullough, Calum Birney, Stephen McAlorum, Jordan Stewart, Johnny Addis, Steven Gordon, Kym Nelson, Danny McKee. Subs: Fra McCaffery (on for McKee, 65 mins), George Gray, Matty Kerr, Adam Calvert, Aaron Hogg.
PORTADOWN: Billy Brennan, Chris Casement, Ross Redman, Keith O’Hara, Peter McMahon, Tim Mouncey, Sean Mackle, Ken Oman, Gary Twigg, Shea Conaty, Robert Garrett. Subs: David Miskelly, Darren Murray (on for Conaty, 39 mins), Jake Richardson, Marcio Soares, Jordan Lyttle (on for Oman, 6 mins).
Referee: Andrew Davey.