Grant conceded a shot he should have saved for Nouha Dicko's opener, but there was far worse to come.
In the 69th minute a cross was floated in from the right which Grant attempted to punch away unchallenged, when he could have caught it.
Inexplicably he got it all wrong, and batted the ball into his own net. It was a calamitous mistake, and one which summed up Derby's evening.
It was the second away loss for Steve McClaren's side in succession, and brings Wolves to within just two points of the Rams.
Derby could be overtaken by Brentford this weekend and Ipswich could draw level on points with them. Right now they are five points off the lead in the Championship and could slip to eight by Saturday evening.
The result was a bitter blow for their automatic promotion prospects and it's clear now the confidence-shorn side are in a scrap just to finish in the play-offs.
Grant's errors were game-changing, but fans were split on whether to back him or slate him after the mistakes. Here's a look at how supporters reacted on Twitter...
#dcfc for me we haven't had a good keeper since mart poom. grant is so confident for such a poor keeper— Paulharton (@harton74) March 20, 2015
Grant should pay for our tickets, ruined the season! #dcfc— Wiiiilllllyyyy. (@Will_Laban) March 20, 2015
Got a lot of contenders for the "Lets blame Grant" club chairman. It's not helping anyone, he knows what he's done. #dcfc— Matt Harvey (@mattharvey07) March 20, 2015
Hang on derby people, Grant is a great keeper I'm sure he's kept us well in these important games one mistake doesn't sum up a player #dcfc— MegaStarly (@MegaStarlyLul) March 20, 2015
This is an absolute joke! Not even gonna make playoffs! Absolute bottlers!! Grant/keogh you absolute tools #dcfc— Matt Delaney (@MattieD3) March 20, 2015
Lee Grant AKA Dracula ( Scared of crosses) Been saying it for a while he's poor. #dcfc— kevin hurd (@kurdy007) March 20, 2015
Grant doesn't deserve any criticism he's saved us so many times, he's allowed the odd mistake #dcfc although it was a clanger— Tom (@dcfctom97) March 20, 2015