Simon Yeo headed Lincoln level five minutes from the end but was then sent off for over-doing his celebrations. Yeo, booked earlier for a foul, stooped low at the far post to steer in a free-kick and earn City a point.
Posh looked to be on course for victory when ex-Imp Peter Gain slammed home a brilliant 30-yard opening goal.
Lincoln keeper Alan Marriott pulled off a fine save to deny James Quinn, and a game played at a fast pace also saw Yeo and Jamie McCombe go close for Lincoln.
Peterborough: Tyler, Holden, Bolland, Plummer, Arber, Newton, Carden, Gain, Day, Quinn (Logan 75), Crow (Willock 63).
Subs Not Used: Farrell, St. Ledger, Huke.
Booked: Crow, Quinn, Holden.
Goals: Gain 30.
Lincoln City: Marriott, Cryan (Stirling 63), McAuley, McCombe, Hughes, Steve Robinson, Brown, Kerr (Frecklington 74), Green, Marvin Robinson (Ryan 74), Yeo.
Subs Not Used: Birch, Foster.
Sent Off: Yeo (86).
Booked: Brown, Hughes, Yeo.
Goals: Yeo 85. Att: 6,227
Ref: T Parkes (W Midlands).