James Perch's second-half header gave Nottingham Forest a share of the points against Birmingham.
The visitors were on course at half-time for their first win in three games after McFadden had opened the scoring.
Lee Carsley's ball into the area was flicked on by Marcus Bent to McFadden, who saw his first shot blocked but then tucked the ball under Lee Camp.
But Forest levelled when the home side failed to clear a their lines and Perch stooped from close range.
Nottingham Forest manager Colin Calderwood told BBC Radio Nottingham:
"It was a slightly nervous start from one or two but we have fantastic potential.
"We got on the front foot and they made mistakes when they were in possession.
"Positionally we were excellent. There were some fantastic individual performances today."
Birmingham boss Alex McLeish:
"We've had a lot of disruptions but I'm not making excuses.
"It was a very poor performance after we scored the goal.
"It was almost as if we waited for something to happen for Forest. When they scored just after half-time there was still plenty of time for us to get back on top but nothing happened.
"I expect better than that from our boys, despite all the disruptions."
Nottm Forest: Camp, Chambers, Morgan, Wilson, Heath, Anderson (McCleary 72), Perch, Cohen, Thornhill, Garner (Martin 82), Tyson.
Subs Not Used: Smith, Breckin, Davies.
Booked: Perch.
Goals: Perch 52.
Birmingham: Maik Taylor, Hunt, Jaidi, Martin Taylor, Ridgewell, Agustien (Jerome 58), Quashie (Phillips 75), Carsley, Larsson, Bent, McFadden.
Subs Not Used: Doyle, Nafti, Owusu-Abeyie.
Booked: Quashie, Jaidi, Agustien, Jerome.
Goals: McFadden 13.
Att: 21,415
Ref: Phil Dowd (Staffordshire).
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