Porter's blast came in the last 11 minutes of their roses clash with Bradford, but it was no more than Oldham deserved after a stylish performance.
The Latics missed a number of chances and were also denied by some inspired goalkeeping from Jamaican international Donovan Ricketts.
But their pressure became too much in the end as Porter bagged his ninth and tenth goals of the season.
Porter and his strike partner Paul Warne were a handful all afternoon and Warne almost struck after just three minutes when his shot from 16 yards had to be superbly turned away by Ricketts.
Andy Liddell blazed over the bar for Oldham before midfield playmaker Richie Wellens was also off target from just inside the box.
Bradford showed a glimmer of attacking spirit after 21 minutes when Marc Bridge-Wilkinson was just off target with a free-kick and Dean Windass shot straight at the keeper.
Oldham, however, were soon back in control and Ricketts performed heroics to tip over a glancing header from Warne.
More chances were wasted by Oldham as their finishing did not match their approach play, with midfield man Chris Taylor missing twice and Wellens again denied by Ricketts.
Bradford had taken off on-loan Crystal Palace winger Tommy Black after just 37 minutes of his debut, but even the pace of ex-Oldham forward Jermaine Johnson did not help them up front.
Oldham's breakthrough stemmed from a fine move down the right involving Warne, Liddell and Wellens, whose astute pass set Warne free in the box.
His low cross reached Porter lurking in the six-yard box for a simple finish past the stranded keeper.
Oldham doubled their lead within three more minutes and Liddell crossed from the right and Porter sent a towering header inside the far post from eight yards.
Bradford almost pulled one back at the death but defender Mark Bower could not beat Aussie goalkeeper Les Pogliacomi.