Louis John put the Yellow Army in front after just four minutes and Omar Bugiel added a second with just over 20 minutes to play.
The victory sees Sutton move up to seventh in the EFL League Two table with their second clean sheet in the last three matches while Mansfield's five-match winning streak in all competitions was brought to an end. They are in 18th position, not currently close to the play-off places or the drop zone.
Story of the match
Sutton came out looking to attack and they were rewarded when a lofted free-kick into the Mansfield box was headed down and bundled home by John to give them the lead.
The hosts nearly doubled their lead soon after the goal when Jonathan Barden chipped into the box and Ben Goodliffe rose to meet it in the six-yard box, but fired over the bar.
Stephen McLaughlin delivered a free-kick that Jordan Bowery got on the end of, but he dragged his half-volley wide.
Sutton went looking for a second and Isaac Olaofe had a chance, but he could only find the side netting.
Mansfield continued to push for an equaliser as McLaughlin's delivery was sent just wide of the post by Ryan Stirk. The full-back then made a goal-saving tackle at the other end, clearing from Ricky Korboa's shot.
The points were wrapped up when Bugiel turned his man in midfield to fire a left-footed strike into the top-flight corner, leaving Nathan Bishop with no chance.
Man of the match: Omar Bugiel
He had a penalty shout waved away in the early stages of the game, but that set the tone for Sutton and his first goal since the opening day of the season capped off a fine display from him and his team.