But they were made to sweat at the City Ground as the visitors did brilliantly to come back from behind and take the tie to extra-time and the dreaded shootout.
The tie appeared to have been put to bed when Brennan Johnson opened the scoring on 19 minutes to put Forest 3-1 up, while the away side lost their cool.
A mass brawl was sparked after Paul Heckingbottom shoved the ball into the lower part of Forest defender Djed Spence's stomach - Heckingbottom receiving a yellow card for the offence.
But Heckingbottom's men were a different team after the break and levelled on the night through Morgan Gibbs-White's classy finish.
And they took the tie to extra time thanks to John Fleck's strike from close range.
Forest goalkeeper Brice Samba made a crucial save to deny the visitors in the closing stages of extra-time.
It was Samba who proved to be the hero as he saved spot-kicks from Oliver Norwood, Conor Hourihane and Gibbs-White to seal a 3-2 win in the shootout.
Forest, who were bottom of the Championship when Steve Cooper took over in September, will face Huddersfield in the play-off final at Wembley on May 29.