Rob Street scored his first league goal for Lincoln as they toppled League One leaders Stevenage 1-0 at the LNER Arena.
His 69th-minute strike inflicted only the second league defeat on Boro, who began the day at the summit, this season as they saw their four-game winning run in all competitions ended in the lunchtime kick-off.
City started well and Ben House slammed Adam Reach's cross wide inside four minutes before Street curled an effort just over.
The same player then should have done better when played through on goal by Tendayi Darikwa but shot tamely wide as Filip Marschall came out to narrow the angle.
It took Stevenage 37 minutes to have their first effort at goal, with Harvey White pulling his effort well wide, before Freddie Draper poked a shot straight at Marschall after a goalmouth scramble at the other end.
Darikwa then had a shot saved by Marschall, with the rebound falling to Reeco Hackett three yards out but he miscued his effort and the chance went begging.
After the break, Boro created a golden opportunity, with Dan Kemp firing Chem Campbell's cross goalwards only for Reach to make a crucial intervention and clear the danger.
City grabbed the decisive goal with 21 minutes remaining following a melee in the Boro box which saw House chopped down but, as he appealed for a penalty, the ball fell to Street who smashed a shot into the top corner.
Match report supplied by PA Media.
