Less than a minute after the turnaround the Latics were handed a way back into the game as Reagan Ogle's long throw dropped to Monthe in the area, only for the big defender to go down under the challenge of Ben Goodliffe in the six-yard box.
Referee Elliot Bell pointed to the penalty spot allowing Garner the chance to coolly slot home, with Hayes diving the wrong way.
Just after the hour mark Fondop had another sight of goal as Corry Evans' skidding shot from 25 yards broke to him in the box, only for Hayes to fly to his left to turn away his low effort.
Keenan Appiah-Forson had appeals for a Shrimpers penalty waved away with just over 20 minutes to play, as Southend finished the 90 minutes the stronger, though Kitching came within a couple of feet of winning it for Oldham with a low strike during nine minutes of added time.
It took less than a minute of extra time for Southend to restore their lead when Appiah-Forson threaded Scott-Morriss through into the box and his looping cross was clawed off the line by Hudson but only for the lurking Chambers-Parillon to nod home at the far post.
Hudson stood firm at his near post to deny Macauley Bonne in the early stages of the second period of extra time, a save which was to prove crucial.
A long ball over the top allowed Norwood to get in behind Goodliffe and he kept his composure to nip past Hayes and slot the ball into the unguarded net.
Bedlam turned to pandemonium within two minutes as Harratt was found on the Latics right and he swung in a curling cross with his left foot which evaded the sliding Goodliffe and sailed inside the far post of the flat-footed Hayes.
The Shrimpers players hit the turf in despair but bounced back up to try and set up a grandstand finale, but the unfortunate Goodliffe missed his kick in the Oldham goalmouth after Nathan Ralph's low cross, and it was to be the last telling action of the contest.
Image source, Getty Images
