Sam Walker and George Moncur were FA Cup heroes for Colchester United as a late penalty save and goal sent the Essex side through to the Third Round.
In a fairly even, but uneventful game, it burst into life in the last five minutes when Peterborough United's Aaron McLean was given the chance to win it for the visitors.
He stepped up when Posh were awarded a spot-kick three minutes from time, but Walker produced a fine save before midfielder Moncur snatched a stoppage-time winner.
Colchester United 1-0 Peterborough United
The FA Cup Second Round Proper
Weston Homes Community Stadium
Sunday 7 December
Colchester receive £27,000 from The FA Cup Prize Fund
And it brought to an end a run of three defeats for Tony Humes' Colchester as their dream of an FA Cup run continues.
The U’s, who were sitting in the League One relegation spots, looked keen to respond from their 6-0 drubbing at MK Dons last time out, and started the brightest.
And although Darren Ferguson’s Peterborough were ten points ahead of their opponents, they were also without a victory since their FA Cup First Round win at Carlisle.
Colchester’s Moncur had the first real attempt at the Posh goal, but his effort was deflected wide for a corner inside the first ten minutes.
McLean, the former England C striker, had a chance at the other end as he was put through on goal, but ‘keeper Walker was equal to a fairly tame effort.
Ex-West Ham United man Moncur was looking lively in the heart of Humes’ midfield. He came very close again to opening the score, controlling a left-foot shot from 18 yards, which forced a solid low save from Ben Alnwick.
Chances were few and far between, however. Craig Eastmond tried a long-range attempt before McLean’s run and cross was dealt with by Walker and it was no surprise the sides headed in with no goals at the break.
A Moncur cross in the opening minute of the second half should have caused more problems than it did as Alnwick claimed with ease, then again McLean had a sight at goal which was blocked then gathered by Walker.
If an opener was to come, McLean looked as likely as anyone to get it as Peterborough took control of the game.
He struck another effort goalwards following a free-kick cut back from the right, but that was blocked. He also smashed a volley from 20 yards that could have gone anywhere, but thankfully for the home side it found the welcoming arms of Walker.
And the Colchester stopper was to prove his worth with two match-winning saves late on. First at full-stretch from Jermaine Anderson’s dangerous drive, but his next denial changed the match.
Sanchez Watt cleaned out Michael Bostwick with a rash challenge inside the box and referee Tony Harrington had no hesitation to award the spot-kick.
McLean took responsibility and did nothing wrong with his penalty, smashing hard and low towards the bottom corner. But Walker reacted superbly to push away for a corner.
It fired the home crowd into life and, spurred on by the Essex faithful, Colchester attacked.
And when an injury-time ball dropped to the feet of Moncur on the edge of the box he calmly stroked home with a cool side-footed effort leaving Alnwick stranded and send Colchester into the hat for Monday’s draw.
Colchester United: 1 Sam Walker, 42 Cole Kpekawa, 18 Tom Eastman, 13 Kaspars Gorkss, 41 Elliott Hewitt, 6 Craig Eastmond, 38 David Fox (c), 24 George Moncur, 11 Freddie Sears, 21 Gavin Massey, 7 Sanchez Watt
Substitutes: 19 Rhys Healey on for 21 Massey 81, 20 Sean Clohessy for 7 Watt 90+3
Subs not used: 12 Chris Lewington, 35 Michael O'Donoghue, 37 Dion Sembie-Ferris, 28 Sammie Szmodics, 27 Macauley Bonne
Manager: Tony Humes
Goal: George Moncur 90
Peterborough United: 27 Ben Alnwick, 25 Gabriel Zakuani, 3 Kgosi Ntlhe, 6 Michael Bostwick, 21 Christian Burgess, 15 Jermaine Anderson, 17 Joe Newell, 10 Erhun Oztumer, 8 Jack Payne (c), 14 Conor Washington, 20 Aaron McLean
Substitutes: 12 Kyle Vassell for 25 Zakuani 90+3, 9 Luke James for 8 Payne 90+3
Subs not used: 22 Ricardo Santos, 37 Leonardo Da Silva Lopes, 2 Michael Smith, 32 Dion Henry, 19 Nathaniel Mendez-Laing
Manager: Darren Ferguson
Referee: Tony Harrington
Attendance: 2,905