Aaron Lennon's strike deep into injury-time ensured that Tottenham Hotspur continued their best start to a league campaign for 49 years. But with four wins from four matches they have a long way to go to emulate the 1960-61 Double winning side, who launched that remarkable season with 11 successive victories.
But Harry Redknapp's men face two of their sternest tests of the season after the international break, when they face Manchester United and then Chelsea. As if that does not seem tough enough, they may be without Ledley King and Luka Modric, who had to go off here with injuries to groin and calf respectively.
Spurs took the lead through Peter Crouch, but after Lee Bowyer capitalised on a defensive mix-up between Alan Hutton and goalkeeper Carlo Cudicini, it seemed the sides would end level.
But there was a late twist as Stephen Carr, who began his career as a Spurs player, lost possession five minutes into injury-time, and Lennon raced away before drilling home an impressive winner.
But manager Redknapp is concerned. "We should have battered them out of sight, shouldnt we?" he said. "We were all over them in the first half and should have got the early goal. Then we lost Ledley King at half-time with a groin injury and then Luka Modric with a calf problem and we were left short.
"I thought Peter Crouch made a big difference when he came on. He was marvellous and was possibly our best player. But then we give away a really silly goal and by the end, after Birmingham got their equaliser, they looked as likely to score as we did. Overall, though, we've got 12 great points.
"I could be looking to bring someone in before the window shuts because we are short. Now we don't see the players again for another two weeks because they are on international duty. We just have to keep our fingers crossed that nobody gets injured. It's ridiculous that we don't see about 10 of them until they come back on the Friday morning before the Manchester United game."
Birmingham felt they could have had a penalty before Spurs opened the scoring in north London. James McFadden, who played on the left of a five-man midfield, went down under pressure from Wilson Palacios, and the visitors were furious that no spot-kick was awarded.
England international Crouch then made a significant impact after replacing Modric – and had five chances to score before he eventually found the net. One header hit the post, another hit the bar, but finally Crouch converted as he steered home a Tom Huddlestone free-kick from the right flank after 71 minutes.
Joy soon turned to despair though, as poor defending allowed Birmingham level. Hutton tried to shield off Blues substitute Christian Benitez but got in a mix up with Cudicini and Bowyer was able to tap into an unguarded net.
Five minutes into added time Carr then lost possession, and Lennon had the last say as he drilled low into the bottom corner after moving inside the Blues' back line.
It was a cruel blow to the visitors, who possibly deserved a point on the strength of their resilience. "It was a bit of a blow to the proverbials," said Birmingham manager Alex McLeish. "But life goes on and I'm proud of the players.
"We are all hurting a wee bit because I thought we deserved something. Stephen Carr is distraught, but it is human error. I still feel we could have defended it better – and we'd had a couple of chances to win the game before then."
Birmingham have now lost both the away games they have played so far, and McLeish is waiting to discover whether he can seal the signature of the Sporting Gijon midfielder Michel.
"We only named six substitutes and that says a lot about our injury troubles at the moment. I'm waiting on word from the Spanish side over Michel. We are working hard to get paperwork in place. We could do with an extra body, without doubt."
Referee: Peter Walton
Man of the match: Lennon
Match rating: 7/10Reuse content