Linfield’s title ambitions were rocked at Windsor Park following a sluggish showing against the Danske Bank Premiership’s basement team.
It took an injury-time equaliser from substitute Josh Carson to salvage a little piece of pride for second-placed Linfield after Adam Foley had shot Portadown into a dramatic lead with only nine minutes remaining.
David Healy’s side now trail title-holders Crusaders by a staggering nine points - with only nine games of the campaign left.
The Linfield boss’ night ended in a dismissal from the dug-out during injury-time. And the home fans obviously felt the title had gone for the fifth successive year as they vented their anger at the players at the finish.
Portadown approached the game, having lost their last six league games, a whopping 12 points adrift of 11th-placed Carrick Rangers. But they displayed a desire and passion that would suggest they could still produce their own version of the great escape.
The Blues thought they had opened the scoring on seven minutes when Jimmy Callacher’s header ballooned the net following a delicious cross from Kirk Millar but referee Lee Tavinder spotted an infringement and ruled out the effort.
Healy’s boys asked all the early questions and ace predator Andy Waterworth almost broke the deadlock with a stunning volley from another Millar cross but goalkeeper Chris McGaughey produced a wonder save, pawing the ball to safety.
The visitors were then gifted a great chance of taking a shock lead. Stephen Lowry’s pass strayed into the path of Foley, who took off on a great 20-yard dash before slipping a clever pass to Marcio Soares, whose low drive was deflected clear by the boot of goalkeeper Roy Carroll.
Waterworth was a constant threat to the Ports’ backline and he almost made the breakthrough just before the interval. This time he picked up a Lowry pass and, after showing a clean pair of heels to his marker, he again poked his shot into the side-netting.
The introduction of Paul Smyth injected fresh impetus into the home team after the interval.
A piece of Smyth wizardry on the right created a great chance for substitute Ross Gaynor, whose point-blank shot was brilliantly blocked on the line by Mark Carson.
It was total domination from the home team and they were right out of luck when giant defender Mark Stafford met a Gaynor corner-kick only to see McGaughey flick his header over the top.
But Foley silenced the home fans with only nine minutes left. Callacher was caught napping in his own box and, when the ball fell, Foley looped an unstoppable shot over the head of a stranded Carroll.
Robbie Garrett almost added a second, only to see his vicious shot pushed away by Carroll.
Linfield threw everyone forward looking for an equaliser, which duly arrived in injury-time when Carson headed home after Waterworth’s shot was saved by McGaughey, who was injured in the process and duly carried off.
Blues boss Healy also finished in the grandstand after being sent off in the dying seconds for speaking out of turn.
LINFIELD: Carroll, Stafford, Stewart, Callacher, Waterworth, Lowry, Millar (Smyth, 46 mins), Clarke, Casement (Carson, 78 mins), Mulgrew, Quinn (Gaynor, 63 mins). Unused subs: Ward, Fallon.
PORTADOWN: McGaughey (Duffin, 97 mins), Carson, Shannon, Larkin, Hazley, Garrett, Henderson, Mackle, Soares (Mulvenna, 80 mins), McGerrigan, Foley.
Unused subs: Duffin, Gardiner, Richardson, Dolan.
REFEREE: Lee Tavinder (Dungannon).