The victory takes McLeish's charges above Reading, who do not play this weekend, and into the automatic promotion places - breathing down the necks of their midlands rivals with a game in hand.
But McLeish, who has received his fair share of criticism of late, remained calm.
"Results make a difference and if we don't get the result I'm a dud and if we do get the result then you're a great manager, you know the fickleness of the game," he said.
"And that's why we have to keep our sanity about the whole thing.
"I know we've stuttered a little bit but we have shown a toughness and I thought this was a very good, above-average performance.
"Forest gave us a few early scares but then we settled in."
Marcus Bent, who had earlier seen his header bounce off the crossbar, put Blues ahead in the 62nd minute when the ball fell nicely in the area following a tussle with Kelvin Wilson and he turned to prod the ball under Paul Smith.
Keith Fahey's first goal for the club wrapped up the points 15 minutes from time.
The Irishman burst down the left and chipped the ball over Smith and into the far corner, although he later admitted it was intended as a cross.
"I was really pleased for Marcus to come in do what he did," added McLeish. "He led the line brilliantly and it was much more like the Bent who terrorised defences in the Premier League.
"Keith's goal was almost 'Messi-like', outside of the right foot and into the top corner.
"It looked a little bit of a fluke, as though he tried to put it across the goal and it landed in the corner, but if anyone deserved a goal for his performance then it was him."
Reds boss Billy Davies felt his young charges were unfortunate to come away with nothing to show for their efforts but was quick to stress he is shaping a team for the future and this defeat will not determine their season.
"I'm disappointed in our lack of ruthlessness, we should have come in at half-time at least 2-0 up," said Davies, who played under McLeish at Motherwell in the mid-to-late 1990s.
"I was pleased with the first 45 minutes, there's no doubt that we took the game to them but we just lacked that ruthless streak, which is the difference between the top and bottom.
"Second half, I thought Birmingham controlled the game better, but how can you condemn my players for the two goals we've lost?"
He added: "This is very much a work in progress. I will look at the loan market and try and add to the squad, but it won't be easy.
"This season is all about keeping our head above water, coming to Birmingham and losing will not define our season.
"I've got no doubt that I've got enough in my ranks to go and get the points necessary."