The Imps were always up against it after falling behind to an early controversial penalty. But they created few chances only showing inspiration when they were already two goals down and reduced to ten men.
The result pushed Lincoln down to fifth place with their results since Christmas giving little hope of finishing in one of the three automatic promotion spots.
Mansfield took the lead after 15 minutes when striker Simon Brown got in front of Lee Beevers inside the box. The Lincoln defender appeared to shoulder charge Brown and referee David Foster awarded the spot-kick despite rigorous protests from Beevers.
The Lincoln man was yellow carded before Barry Conlon sent Alan Marriott the wrong way with a well-struck penalty.
When Lincoln tried to hit back Dany N'Guessan set up Jeff Hughes but the midfielder shot narrowly over the bar.
Lincoln looked to have won a penalty themselves in the 33rd minute when Lee Frecklington forced his way through three tackles before appearing to be chopped from behind by Stephen Dawson. This time Mr Foster waved play on.
The official's decisions infuriated the home fans with both Adie Moses and N'Guessan unlucky to earn yellow cards.
Mansfield continued to create the better chances and Brown should have scored in the 47th minute when he broke clear only to shoot straight at Marriott.
Four minutes later Lincoln were again caught out by Brown's pace down the left. The winger beat his man before crossing for youngster Nathan Arnold to score an easy goal.
Brown should have put the result beyond doubt on the hour when he got past Moses, but with the goal at his mercy he somehow shot into the side netting.
Lincoln's Beevers was dismissed a minute later following a foul on Brown as the striker tried to go past him.
City responded by bringing on Owain Warlow and the teenage winger set up Lincoln's consolation goal 16 minutes from time when his excellent cross from the left was netted by Jamie Forrester.
Lincoln could have had an equaliser six minutes later when Hughes cut inside from the right only to see his well struck shot saved by Town keeper Jason White.