Striker Grabban scored twice to take his season’s tally to eight and could have had more having missed a third spot kick since joining the club in the summer.
He has scored the other three of six penalties Forest have been awarded this campaign and has twice now dusted himself down to convert after missing an earlier one from 12 yards.
And Reds boss Karanka praised his £6m front man.
He said: “Sometimes when you miss a penalty it is hard to take the next one but Lewis always wants to take the ball. He’s a strong character and he trusts his own ability so it is important for us to have a player like this in our squad.
“I’ve thought about changing the penalty taker but Lewis took the ball so I backed him all the way. He’s happy and confident and you can tell that rubs off on the rest of the team.”
Karanka was delighted with the response of his players at the University of Bolton Stadium after Saturday’s disappointment at home to Norwich City.
“It was a really good performance,” Karanka added on Wednesday night. “From the first minute we played well and we showed that Saturday was forgotten about.
“In the second part of the first half we dropped off a bit but the second half was much better and I think it was the perfect response.”