Posh boss Darren Ferguson hailed his team of comeback kings as he celebrated the best promotion of his managerial career.
Peterborough only needed a point to seal the deal but it looked a long way off when they fell 3-0 down to a Lincoln side that could still catch them in second place.
The recovery started five minutes after the hour, with Siriki Dembele opening Posh's account, and was capped by a last-gasp penalty from Jonson Clarke-Harris.
The penalty decision itself was controversial, with Lincoln manager Michael Appleton left seething at the outcome after Sammie Szmodics went down in the box.
But for Ferguson it was all about his players producing a remarkable comeback to clinch a Championship return after eight seasons in the third tier.
Speaking after the game, he said: "It’s absolutely incredible. I’ve never seen anything like it.
"This club means so much to me and there is no doubt this is the best promotion I’ve ever had. I don’t mind admitting I got quite emotional after such a tough couple of seasons. We worked too hard for it to blow it.
"I had all sorts going through my mind at 3-0 down, but what a bunch of players I have. To do what they did in a game of such magnitude is fantastic.
"I always felt we could come back if we just got one goal. We did that and then after the second goal I thought we would go on to win it, never mind draw.
"That didn’t happen and we ended up hoping for one more chance. When it came I knew Jonson was going to score. The boy has been an unbelievable signing. To smash the penalty in the way he did under that much pressure was brilliant.
"We’re in the Championship again and we’ll be trying our best to stay there."
Meanwhile, Imps boss Appleton was left aggrieved after his team were denied the win they needed to keep second place in their sights.
"If I called it anything less than an absolute disgrace, I probably wouldn’t be doing it justice," he said after the whistle.
"We knew when we got 3-0 up that Peterborough would have absolutely nothing to lose and that made them dangerous in terms of their attitude. Losing 5-0 would have made no difference to them at that point.
"We missed a sitter at 3-1 and I started to wonder if it was going to be one of those days.
"Conceding the free-kick for Peterborough’s second goal was disappointing as there was a bit of a turtleneck going on and that shouldn’t have happened. But it has all come down to a decision that is completely undefendable.
"There is genuinely no-one in the ground who would say any different and it is really frustrating. The referee must have a Peterborough postcode.
"We firmly believed we could go on to win our final two games and put all the pressure on Peterborough.
"We have a young group who are only going to get better and use this experience to make sure we’re doing the celebrating in the future."