It also stretched their record under new manager Steve Thompson to only one defeat in 14 league and cup games this season.
Dudfield, who replaced Jason Lee ten minutes from time, powered home left-back Austin McCann's cross to snatch all three points from a dour match which had the look of a goalless draw.
With both teams visibly determined not to make a damaging mistake or over commit themselves, there were few chances or goalmouth incidents and precious little entertainment.
Torquay had signed veteran target man Leo Fortune-West as a replacement for the injured Mickey Evans, but the former Gillingham and Doncaster striker could give in-form Jamie Ward few chances to stretch his run of six goals in seven games.
Fortune-West and Lee Mansell both missed half chances in the first half, before Mike Edwards squandered the best opening, miskicking with only keeper Nathan Abbey to beat from a McCann free-kick.
Torquay tried swapping striker Ward with winger Chris McPhee in an effort to pep their attack, but they could find little inspiration and it took a 25-yard drive just over by midfielder Adam Murray to lift the fans just before half-time.
In the 55th minute Fortune-West forced an acrobatic save from County goalie Kevin Pilkington, heading for goal after Dan Gleeson had skied a Ward cross.
Both sides made attacking substitutions in the last half-hour, but it wasn't until Dudfield took the field in the 80th minute that County started to believe that they might win.
They forced the pace in the closing stages and, when McCann took advantage of some less than decisive defending on Torquay's right, Dudfield was there to finish his near-post cross.
It was the sixth goal that Torquay have conceded in stoppage time this season, costing them at least eight points in the process.