Birmingham were on the attack from the start, with David Cotterill firing just wide inside the opening two minutes, while Demarai Gray had an effort cleared off the line moments later.

Forest's first chance came just before the quarter-of-an-hour mark when Henri Lansbury tried to find the bottom corner, but his curling finish went just wide.

The home side continued to enjoy the majority of the possession, but it was Birmingham who opened the scoring 10 minutes before half time when Cotterill drilled a free kick in low from just outside the box.

The visitors needed just three minutes to double their lead as Cotterill tried another low shot on which Clayton Donaldson got the final touch, flicking it past Karl Darlow.

Donaldson was on target again before the break when Darlow palmed an Andrew Shinnie effort into the bath of the striker, leaving him with a tap in to extend the lead and pile the misery on Forest.

The hosts at the City Ground had a chance to pull one back just moments after the restart, but Jamie Paterson's volley ended up in the side-netting after a quick break.

Forest had another opportunity shortly after when Paterson won a corner for Stuart Pearce's side, but Robert Tesche flicked wide from just a few yards out.

Birmingham almost ended any hopes of a second-half comeback when Cotterill sprinted down the wing before cutting inside to curl the ball in, but Darlow made the save.

Gray also had a chance to extend the their lead, but the Forest keeper was ready again to punch the teenager's effort clear.

The home side added a late consolation when Britt Assombalonga headed in from Ben Osborn's cross at the start of stoppage time.

The result moves Birmingham up to 14th in the table, while Forest remain 10th.