A dreadful attempt at a back-pass by Will Haining in the third minute resulted in Akpo Sodje being given a free shot at goal, but some awful finishing allowed Les Pogliacomi to save low to his left.
Paul Warne's darting run to the by-line troubled the Vale defence in the 13th minute when his cut back pass set up Gary McDonald, but the final effort lacked enough quality to hit the target.
John Sheridan was forced to make two early substitutions with both Stefan Stam and Craig Rocastle limping from the field of play to be replaced by Paul Edwards and Kelvin Lomax.
The Valiants ripped apart the Latics defence in the 18th minute when after some impressive build-up play, Malvin Kamara's low cross found Danny Whitaker lurking inside the box and he coolly slotted the ball past the goalkeeper.
After a long spell of little action for Oldham, Warne took matters into his own hands when he broke free from Danny Sonner's attentions to fire a dipping shot barely over the crossbar from 20 yards.
The home side doubled their lead only four minutes after the break when Sonner's left-footed cross picked out George Pilkington to head the ball just inside Pogliacomi's right post from 15 yards.
Chris Porter could have rescued his flagging side with two quickfire goals, but the striker failed to capitalise on both point-blank chances, leaving Oldham seemingly dead and buried.
Sheridan's miserable night came to a premature end when his remonstrating with the referee was deemed enough to send the manager into the stands for the remainder of the game.
Just when the game looked to have settled down, Sodje's forward run past Pogliacomi was cut short with the goalkeeper flooring the pacy attacker to earn himself a straight red card in the 78th minute.
With the visitors having made all of their substitutions, it was left to Leon Constantine to stroke the resulting penalty past the deputising Chris Taylor to tie up the match.