Late drama in the Boxing Day derby is fast becoming as common as, well, Christmas - with Saturday’s frantic finish the third successive festive fixture to feature a last-gasp goal.
For almost 20 years the Mid-Ulster showpiece provided a degree of predictability as the Ports enjoyed an unbeaten run from 1997 up to 2013.
However, Mark Patton’s strike settled the 2013 clash in the favour of Glenavon and an Eoin Bradley penalty kick secured a share of the spoils last season at Shamrock Park.
On Saturday, it was the turn of Rhys Marshall to write his name into Glenavon’s festive folklore as the young defender forced home a loose ball inside the penalty area with goalkeeper David Miskelly on the ground after colliding with team-mate Chris Casement during a 92-minute corner-kick.
The second-half exit of Michael Gault - following two bookings inside four minutes around the hour mark - handed Glenavon extra incentive for the closing stages. The dismissal of Tim Mouncey as an unused substitute for his protests at the Gault red also left Portadown restricted to just two outfield teenage options to come off the bench.
The pressure eventually produced a decisive moment but Portadown can point to key sights of goal squandered during a derby date that lacked overall quality but featured plenty of spirit - with, in particular, club captain Keith O’Hara superb as an emergency right-back and Ken Oman commanding in the centre of the defence.
Gary Twigg was presented with the first clear scoring opportunity but he steered his header just past the post off a Casement free-kick.
Twigg, so impressive in terms of overall work-rate this season, was forced off with injury, however, on 25 minutes.
His replacement, Mark McAllister then had a golden sight of goal in the second half following a delicious delivery by left-back Ross Redman. However, the striker failed to guide his header on target from an unmarked position inside the penalty area.
Glenavon held the upper hand overall in terms of possession but failed to find a regular path past the organised and resolute visitors, with Portadown frustrated by an unsuccessful first-half penalty shout.
David Miskelly produced stops off attempts by Andy Kilmartin, Marshall and Eoin Bradley - with a perfectly-timed Redman block diverting away Daniel Kearns’ curling effort.
Andy Hall cleared the crossbar from distance and Bradley managed to match that outcome from just a few yards inside the packed penalty area.
However, the final seconds almost featured a Portadown equaliser but Casement’s sidefoot shot was blocked on the line by the covering Simon Kelly.
It marked a second successive derby defeat for the Ports, in the aftermath of a 3-1 defeat on the road in the previous fixture with Dungannon Swifts.
It also signalled a disappointing finale to 2015 and loss in what is expected to prove a final Boxing Day Mid-Ulster derby for manager Ronnie McFall.
PORTADOWN: David Miskelly, Keith O’Hara, Ross Redman, Chris Casement, Garry Breen, Sean Mackle, Darren Murray, Ken Oman, Michael Gault, Gary Twigg, Robert Garrett. Subs: Billy Brennan, Tim Mouncey, Matthew Parker, Mark McAllister (on for Twigg, 25 minutes), Christian Stewart.
Referee: Ian McNabb.