Paterson lobbed keeper Lee Grant from just inside the area three minutes from time from substitute Duane Holmes's through ball.
The former Burnley hitman nearly won it for the home side seconds later but fired wide from a tight angle after being put in by Danny Ward.
Derby had led from the 30th minute, when Craig Bryson scored a close-range tap-in.
In a strong closing spell for Town, Derby were lucky not to concede a penalty when Ward was felled in the box.
Huddersfield, who pepped up with the introduction of Holmes on 58 minutes, also went close twice in stoppage time.
Defender Murray Wallace headed over a Ward corner and then the Town winger saw his stinging 35-yard blockbuster tipped over the bar by Grant.
But until game-changer Holmes came on, Derby had seemed set for an eighth straight win under new boss Steve McClaren.
Midfielder Bryson scored for the fourth successive game with a tap in to put the visitors ahead on the half hour mark.
The former Kilmarnock ace, who now has 11 goals for the season, converted Chris Martin's knock down from Andre Wisdom's curling byline cross.
The effort came soon after Derby missed a penalty awarded on 26 minutes for a foul by Huddersfield substitute Joel Lynch on Jamie Ward.
Keeper Alex Smithies, making his 200th appearance for the Terriers, dived low to his left to parry Martin's spot kick.
The stopper got up quickly to save Martin's hooked rebound and then instantly set up a Huddersfield attack at the other end.
Paul Dixon romped down the left flank and crossed for Paterson, whose shot was deflected over for a corner.
Lynch, who replaced the injured Anthony Gerrard on 22 minutes, nearly scored an own goal before half-time.
He diverted a Martin cross onto his own post but cleared the ball for a corner when it rebounded back to him along the goal-line.
Derby defender Michael Keane had a bullet header from a Bryson cross ruled out for off-side on 65 minutes.
The 20-year-old was making his first start on loan from Manchester United in place of injured skipper Richard Keogh.
Holmes then came on and turned the tide in Huddersfield's favour. He even created an opening from Town's best move of the match.
He beat two defenders near the right byline and pulled the ball back only for Ward and Adam Clayton to see their shots blocked.
Huddersfield, missing influential skipper Peter Clarke and striker James Vaughan through injury, kept plugging away through Holmes.
The Terriers got their reward when Holmes played a one-two with Clayton and then set up Patterson for his stunning lob.