James McFadden scored from the penalty spot in the first half to earn Birmingham victory at Ipswich.
McFadden stepped up to convert from the spot after Moritz Volz was judged to have handled Kemy Agustien's cross.
Jon Walters went close at the start of the second half but his low shot sailed a few yards wide before fellow substitute Darren Ambrose went close.
Agustien came close to grabbing a second for Birmingham but Richard Wright produced a fine save.
Ipswich Town manager Jim Magilton:
"For 30 minutes we were very good. We passed the ball well but lacked a bit of quality around the box.
"It was a soft penalty. I haven't seen it again and I don't want to, but it looked pretty soft. Birmingham are a real Premier League team and they saw the game out.
"Had we got our noses in front it might have been a different story. They've got enough about them and strength in depth, but it was a game of very few chances and neither goalkeeper had a save to make.
"We lost a bit of impetus after Danny Haynes went off but should have come out with all guns blazing in the second half. As it was, we didn't have enough on the day to disrupt them."
Birmingham City manager Alex McLeish:
"After back-to-back defeats, the boys were a bit edgy and this is a difficult place to come, but we showed a lot of character.
"The defence and goalkeeper showed resilience and were delighted to keep a clean sheet - I know I always did, as a defender. It's as important for them as it is for a striker to score a goal.
"Psychologically it's always nice to be in the top two. We are third but the most important thing is to be there when it matters at the end of the season and churning out results like this will certainly help."
Ipswich: Richard Wright, Volz (Counago 75), Campo, McAuley, Thatcher, Norris, Miller, Quinn (Ambrose 59), Haynes (Walters 28), Lisbie, Stead.
Subs Not Used: Supple, Balkestein.
Booked: Quinn, Volz, Miller.
Birmingham: Maik Taylor, Parnaby, Jaidi, Queudrue (Hunt 65), Murphy, McFadden (Bent 69), Carsley, Ridgewell, Johnson, Agustien, Jerome.
Subs Not Used: Doyle, Phillips, Owusu-Abeyie.
Booked: Parnaby, Ridgewell.
Goals: McFadden 39 pen.
Att: 23,536
Ref: Iain Williamson (Berkshire).
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