Substitute Declan Frith scored the winner in the 94th minute as Posh made it four wins from four with a 1-0 victory over Leyton Orient at the Weston Homes Stadium.
The club's 3,000th league fixture proved to be memorable as a late winner from Declan Frith, his first goal for the club, secured a 1-0 win over Leyton Orient to move Peterborough United into 13th place in the League One table.
It was a fourth successive win for Luke Williams' side and means the boss has collected 18 points from a possible 24 since taking over the reins at the end of October.
In truth, it was a game that lacked quality at times, but in terms of opportunities in front of goal, it was Posh who created the better opportunities in front of goal.
However, it was Orient who had the first chance of the game, Dom Ballard rattling the base of the post after finding space in the Posh defensive third.
On 14 minutes, Kyrell Lisbie was a whisker away from breaking the deadlock, but his curling shot went past the upright. Matt Garbett saw an effort pushed around the post by Simkin after a strong run on 38 minutes.
Kioso fired over with his left-foot on 40 minutes while Garbett also cleared the crossbar as Posh ended the first half strongly. Harry Leonard failed to get a shot on target two minutes after the bench after good work from Garbett.
On 48 minutes, Alex Bass made a fine save at his near post to keep out Mitchell's angled drive before Garbett's free-kick was parried by Simkin.
On 73 minutes, Bass pushed a low effort around the post after a strong run and effort from O'Neill. On 74 minutes, Posh were awarded a spot-kick after an apparent handball, but after discussions with the assistant referee, the official, Abigail Byrne reversed her decision and gave the visitors a free-kick.
Leonard found the side-netting on 83 minutes before Johnson tested Simkin from the edge of the box. Four minutes of added time was signalled by the fourth official and in the last minute, Posh found the winner as FRITH headed home from close-range.
Posh: Bass, Johnston, Collins, Lees, Woods (sub O’Brien-Brady 65min), Lisbie Morgan (sub Frith 55min), Okagbue, Leonard (sub Lindgren 84min), Garbett, Kioso. Unused subs: Reyes, Hayes, O’Connor, Dornelly.
Leyton Orient: Simkin, Simpson, Happe (sub James 46min), O’Neill (sub Koroma 80min), Mitchell (sub Adaramola 54min), Craig, Bakinson, Beckles, Moorhouse, Wellens (sub Jaiyesimi 89min), Ballard. Unused subs: Cahill, Abdulai, Jaiyesmi, Clare.
Half-time: Peterborough United 0-0 Leyton Orient
Full-time: Peterborough United 1-0 Leyton Orient
Attendance: 9,882 (759 Orient fans)
Referee: Abigail Byrne