The Blues manager tasted defeat for only the second time since returning to St Andrew’s when they were hammered 4-0 by Derby on Boxing Day.
But two goals from Clayton Donaldson and another from David Cotterill, all in a 10-minute spell prior to the interval, helped stretch Forest’s miserable run of form to two wins in 17 games, with Britt Assombalonga’s 91st-minute header no more than a consolation.
Rowett has now won six of his 10 games in charge to lift Blues well clear of the relegation zone, while Pearce finds himself needing to address a frustrating Forest slump.
It was Birmingham who piled on a short flurry of early pressure, with Cotterill firing a shot into the side-netting and Demarai Gray twice coming close.
Henri Lansbury, restored to the Forest side after illness, was a whisker away from a goal in the 13th minute, as he followed up a burst of short passing on the edge of the box with a low shot that was close.
Matty Fryatt then had his head in his hands after getting a tiny bit too much power on his header, after connecting with a fine cross from Michail Antonio.
Assombalonga twisted and turned his way into the box beautifully, only to be denied by a smart save from Darren Randolph and, when the ball ricocheted loose to Lansbury, his rocket of a shot was deflected just wide. From the resulting corner, Michael Mancienne headed over.
It had looked as though it was Forest who would take the lead, but it was Birmingham who struck first. Lansbury brought down Gray as he threatened to cut into the box from the left, to collect his 10th booking of the season and concede a dangerous free-kick. And Cotterill took full advantage, somehow finding the bottom corner of the net with a low shot through a crowd of players.
That goal came in the 35th minute and three minutes later Birmingham doubled their advantage. Cotterill was again an integral figure has he drove in another low shot which found the bottom corner of the net, this time with the aid of a slight touch from Donaldson who was quick to claim the goal.
The game was all-but killed off just before the interval when Donaldson pounced on a deflection to scramble the ball past an exposed Darlow to give Birmingham a 3-0 advantage, although Robert Tesche did clatter the crossbar with a spectacular strike that bounced down just the wrong side of the line for Forest.
Tesche came close again after the break, this time with a header, as Forest looked for a way back into the game, by forcing a sustained spell of pressure. But Birmingham were doing a decent job of seeing the game out, with Cotterill even coming close to a fourth with a 20-yard shot that Darlow held well.
A corner from sub Ben Osborn picked out Assombalonga at the far post for the striker to head home a consolation goal in injury time, but it was too little too late for the hosts.