Latics trailed at half time through goals from Lee Angol and Erhun Otzumer before Rhys Murphy pulled a goal back early in the second half.
Souleymane Coulibaly grabbed a second half double before Angol rounded off the scoring as Latics suffered their second successive home league defeat.
It was a concerning start to the game as Mark Yeates went down clutching his lower back but the winger was okay to continue.
Latics were playing some neat football around the edge of the box but were struggling to penetrate the Peterborough defence.
It was almost a disaster for number one goalkeeper Joel Coleman on 10 minutes as he was chased down a loose ball on but as he tried to shepherd the ball out of play, he was dispossessed.
Coulibaly raced away with the ball but luckily Yeates got back to guide the ball out for a corner, which was eventually cleared.
The former Bradford City and Watford man was at the centre of most of the action and he forced Posh goalkeeper Ben Alnwick into a save on 12 minutes as he struck from 25 yards.
The visitors did take the lead on 14 minutes through Angol.
Coulibaly picked out the striker, who was in acres of space on his own in the centre, and he tapped home from five yards to give Posh the advantage.
Latics needed a response and almost pulled level midway through the half but David Dunn’s strike from 18 yards was saved well by the Posh stopper.
Athletic started to play the ball with more conviction and kept the ball well in dangerous areas but again the final ball was letting Latics down.
Yeates fired over the crossbar after the half hour mark whilst at the other end Peterborough midfielder Marcus Maddison struck over from 18 yards.
The visitors doubled their advantage on 38 minutes in similar fashion to their first goal.
This time Oztumer received the freedom of the penalty box and he met a cross from Angol and fired into the top corner to make it 2-0 to the visitors.
Latics needed half time to regroup but almost got back into the game before the break. Rhys Murphy chased down a through ball but Posh just managed to clear their lines as Latics went into the half time break two goals behind.
There must have been stern words inside the Athletic dressing room at half time as they came out firing in the early part of the second half.
Carl Winchester struck the post from 18 yards before Latics did get back into the game with a sumptuous strike from Murphy.
The striker received the ball on the edge of the box and blasted into the top corner to reduce the arrears.
Latics were really on top and were taking the game to their opponents with Dunn and Winchester pulling the strings to the attacks.
Eoghan O’Connell rose highest from a corner but headed over the crossbar whilst Stankevicius stung the palms of Alnwick from 12 yards.
Just after the hour mark, and slightly against the run of play in the second half, Peterborough regained their two goal advantage as Coulibaly struck.
The forward, who caused Latics problems all afternoon, was played through on goal and made no mistake from 18 yards, firing past Coleman.
Three minutes later it was 1-4 as Coulibaly got his second of the game, heading in at the far post from a cross into the box.
Latics were shellshocked but were determined to get back into the game.
Yeates’ free kick from 25 yards was tipped over the crossbar whilst substitute Dominic Poleon struck the post from the edge of the box.
Peterborough United made it five on 78 minutes as Angol guided into the bottom corner after a cut back into the box from Coulibaly.
With less than 10 minutes remaining, Dunn fired from 25 yards which forced a smart save from Alnwick and at the death, substitute Mike Jones struck a free kick over the crossbar.
Oldham Athletic: Coleman, Brown (Dieng 45’), Wilson, O’Connell, Mills, Philliskirk, Winchester, Yeates (Jones 70’), Dunn, Murphy, Stankevicius (Poleon 64’).
Subs not used: Croft, Cornell, Burn, Turner.
Peterborough United: Alnwick, Smith, Zakuani, Oztumer (Da Silva 84’), Maddison (Taylor 77’), Almeida-Santos, Anderson, Angol, Coulibaly, Elder, Forrester (Collison 70’).
Subs not used: Henry, Washington, Anderson, Davey.
Goals: Oldham Athletic (Murphy 48’) 1-5 Peterborough United (Angol 14’, 78’, Oztumer 38’, Coulibaly 62’, 65’)
Attendance: 3,566 (220 visiting supporters)