Substitute Brice Ntambwe's second-half winner separated the two sides as a fine performance from Karl Darlow between the visitors' sticks prevented a more comfortable scoreline for Blues.
Blues gave overage trialists Paul Robinson and Bilel Mohsni a run out, while Forest named the experienced duo of Jonathan Greening and Chris Cohen in their starting XI. The hosts also had Colin Doyle in goal.
After an even start to to proceedings, the hosts opened the scoring on the half-an-hour mark through the towering presence of Mohsni. The French-Tunisian, on trial from Southend United, got on the end of Jack Deaman's free-kick from the left to divert the ball beyond Darlow.
Forest were level seven minutes later. A clever throughball from Kieran Wallace found Morgan Ferrier who equalised with a smart finish inside the box.
The away side should have gone in ahead at the interval as they were awarded a penalty on the stroke of half-time. Mohsni clumsily brought down Cohen in the area and Robbie Findley stepped up only to see Doyle easily save the spot-kick.
Richard Beale's Blues stepped it up a gear in the second-half and were easily the better side. Akwasi Asante tested Darlow on several occasions with the best chance coming in the 63rd minute. Tenacious tackling from Mitch Hancox freed Ryan Higgins down the right and his pinpoint delivery picked out Asante yards out yet some how Darlow tipped the effort behind.
However Blues eventually found the breakthrough in the 69th minute. Ben Gordon's corner from the right was aimed for the head of skipper Will Packwood but fell to Ntambwe (pictured) to tap home from close range.
After three straight wins, Blues now sit top of the PDL 2 North with 10 points from the first 12 of the campaign.
Blues U21s: Doyle; Deaman, Robinson, Packwood (C), Gordon; Higgins, Mohsni (Ntambwe 66), Reilly, Hancox; Hawker; Asante.
Subs not used: Preston, Delfouneso, Brown, Ebanks.
Goals: Bilal Mohsni (30), Brice Ntambwe (69).
Nottingham Forest U21s: Darlow, Gregory, Andrews (Gorman 75), Greening, Fenton, Regan, Wallace, Cohen, Findley, Ferrier, Osborn (Blake 75).
Subs not used: Papworth, Smith, Palmer-Samuels.
Goals: Morgan Ferrier (37)