City manager Gary Johnson had been critical of his team after they lost at Birmingham on Wednesday but could have no complaints about the attitude and commitment of his players, apart from the end product.
Nicky Maynard missed two inviting openings in the first nine minutes and Lee Johnson also fired wide from close range.
There were also strong claims for a penalty when Derby central defender Lewin Nyatanga appeared to use his hand to keep out a Johnson free-kick and City's giant centre-back Jamie McCombe headed against a post.
But for all their control and slick passing, City failed to create many clear chances in the second half and, although Derby were under pressure, goalkeeper Stephen Bywater had few shots to deal with.
In fact the home side had some excellent chances on the break to add to Porter's 50-second goal - Derby's quickest of the season - after Mile Sterjovski had set him up from six yards.
They defended that lead until the 83rd minute when City finally found a finish to match their approach play.
The excellent Gavin Williams saw the ball drop to him 25 yards out and his right-foot volley dipped past Bywater and into the bottom left corner.
It should have earned his side at least a point but, for the second time in the game, City switched off and were punished in the 85th minute.
Gary Teale got to the by-line on the left and whipped in a cross which City failed to clear and Hulse showed sharp reactions to stab in his 15th goal of the season to move Derby a step closer to Championship safety.