They created a stack of openings and hit the woodwork three times alone in the first-half.
The decider came in the 87th minute, with Bellingham sliding in to force the ball over the goal line after pressure by Kyle McFarlane on the ‘keeper diverted the ball into his path.
It was quite a moment for the 15-year-old, who entered proceedings on the hour as substitute – replacing another young buck, 16-year-old Kyle Hurst.
Blues had to negotiate a difficult start on a wet and miserable afternoon by the Trent.
Forest got a clear sight at goal in the seventh minute when Blues were opened up on the right but Michael Luyambula made a good save with his legs from Kostas Megaritis.
Blues settled and proceeded to dominate the rest of the first period.
In the 17th minute, McFarlane slipped in Anderson whose low shot hit the ‘keeper’s body and moments later McFarlane forced Tim Erlandsson into a full stretch stop with an angled drive.
That tended to set the pattern, as the next major moment came from a corner that Blues kept alive; Geraldo Bajrami got free on the right and his powerful shot at goal deflected off the incoming Anel Ahmedhodzic and off the face of the crossbar.
Ahmedhodzic, in an almost carbon copy incident, denied Bajarmi minutes later with another last-gasp block.
Blues hit the woodwork again in the 33rd minute when Cameron McGilp steadied himself and curled a sidefooter onto the post after being teed-up from a corner by Bajrami.
Another clear opening, coming after high pressing on Adam Yates, was forced by Blues, with Hurst moving the ball forward to McFarlane who shifted it out to the excellent Olly McCoy, who was arriving free on the right at speed – but once more the shot was saved.
The last action before the break was Ryan Burke letting fly from more than 25 yards on the left and seeing his speculative effort crash into the crossbar, down and out.
Blues – firm and resolute at the back and the front pair working well – continued in the same vein in the second period.
A backpass that was played blind was seized upon, with McFarlane and Caolan Boyd-Munce going in; the ball spun loose, was taken round the ‘keeper by Anderson and Ahmedhodzic did superbly to come round on the cover and slide it from the goal line. For his troubles, he collided with the upright and had to be taken off on a stretcher.
Bellingham replaced Hurst in the 60th minute and played up behind McFarlane, Anderson moved to the left flank.
Forest came more into the game and Blues had to dig in for spells.
In the 76th minute Jake Taylor took the ball off Burke as he tried to turn inside him, scooted down the right and crossed for Virgil Gomis to head strongly at goal from close range, but Luyambula was equal to it, showing agility to parry the effort away.
With five minutes left Boyd-Munce knocked a lovely pass down the left channel for McFarlane to elude the Forest backline but he slightly overran it and Erlandsson was swiftly off his line to smother.
Blues may have thought that was it, a PDL stalemate beckoned. But no.
From a throw back to the ‘keeper, McFarlane chased down, forced a mistake and the ball skidded out to Bellingham, in the middle of the area.
The ball nipped up at his shin as he went to take a touch and although a defender was coming round from the side to try and clear, Bellingham was the more determined to make up the yards and get there first, to prod it home as they both went in for the challenge.
Blues: Luyambula, Forrest, Burke, McGilp (Redmond 79), Bajrami, Martin, McCoy, Boyd-Munce, McFarlane, Anderson, Hurst (Bellingham 60). Subs not used: Siviter, Amartey, Dawes.