It was far from the ideal introduction to the competition for Blues boss Alex McLeish, but the Terriers' all-action display was a textbook example of the kind of upset for which the cup is famed.
The afternoon started well for the hosts when Luke Beckett prodded home from close range and although Garry O'Connor drew the Barclays Premier League side level before the break, the impressive Brandon volleyed home emphatically to seal the win.
• Ritchie hails mammoth effort
The Terriers handed James Berrett a debut in midfield and the youngster had a satisfying first touch, dispossessing Fabrice Muamba in the centre circle with a well-timed challenge.
Then, after just three minutes, the hosts were ahead.
Danny Schofield took possession in a deep-lying position but was not tackled as he strode into Birmingham territory.
He made light work of Radhi Jaidi's attempted block and after a quick give-and-go in the penalty area, he unleashed a shot at Maik Taylor.
Taylor spilled the scuffed effort, but Beckett was first to the loose ball and he stabbed home into an empty net to kickstart the home crowd.
After 13 minutes Town goalkeeper Matt Glennon was on hand to save Mikael Forssell's low drive at the near post.
Brandon, meanwhile, was causing problems at the other end and twice earned corners by attacking the static City defence.
But a quick break following a corner drew the visitors level in the 20th minute.
Taylor set Daniel de Ridder free down the left and he played in Fabrice Muamba, who shrugged off Robbie Williams' attentions to make room for a shot.
Glennon got a firm hand to it, but when the ball broke, it found O'Connor, who slotted home with ease.
The equaliser steadied Birmingham and only a linesman's flag stopped them taking the lead after 24 minutes.
De Ridder was again the architect, breaking at pace and curling a cross high into the Huddersfield penalty box.
The ball took a deflection on its way to O'Connor, who poked his shot past Glennon on the volley before seeing his celebrations cut short by an offside verdict.
The match remained open and the home team continued to play their part, Beckett and Malvin Kamara combining to give McLeish's side another scare after half an hour.
Franck Queudrue was booked for a messy-looking lunge at Kamara and when the lively Brandon climbed highest from the resulting free-kick, he was unfortunate to be denied by a combination of Taylor and the woodwork.
Immediately after the restart a hopeful punt up field landed at the feet of O'Connor 20 yards out, but he could not force a meaningful save from Glennon.
Joe Skarz, a half-time substitute, presented Town with their first chance of the second half, fizzing a cross in from the left and finding the unlikely figure of Andy Holdsworth in the six-yard box, but the skipper made a hash of the finish as the goal beckoned.
Birmingham then took the initiative, Gary McSheffrey and O'Connor both having passable shots.
McLeish took the opportunity to build on his side's momentum by introducing Cameron Jerome - who played for the Terriers as as schoolboy but whose relationship with the club has soured since - in place of Forssell. Predictably, the striker was treated to a chorus of boos.
The former Cardiff man immediately offered a different threat, harrying the defence with pace and brawn, but the crowd delighted in an overhit first touch which sent the ball skidding out of play.
McSheffrey, not impressing on Birmingham's left despite plenty of possession, was gifted the ball on several occasions in the closing stages but produced little of note.
Jerome also fluffed his lines again, rolling the ball into touch when attempting a simple pass.
Instead, it was Brandon who was left to claim the winner.
Beckett, clearly tiring but charging manfully down the wing, heaved a cross deep into the danger area.
As Liam Ridgewell and Jaidi were pulled to the near post, Brandon was given space at the opposite upright to drill home his volley.
Ritchie hails mammoth effortTriumphant Huddersfield manager Andy Ritchie hailed his side's thrilling FA
Cup third round victory over Barclays Premier League Birmingham but insisted
celebrations would last just a day.
'We rode our luck on one of two occasions but we had the chances. It's
fantastic for the town, the fans and not least the players.
'But it's back down to earth on Monday,' said Ritchie, whose side came into
the match 14th in Coca-Cola League One and reeling from consecutive defeats to
Nottingham Forest and Northampton.
'I think that result challenges us to reproduce that form in the league -
that's what I'll be saying to the lads in the week.
'Phil Jevons was suffering with a thigh strain and we left him on the bench
because, to be honest, we were trying to protect one or two because the league
is our main focus,' said Ritchie.
'They are a really good side but they have a big challenge in their own
division and we now need to start climbing up our own division.'
But while Brandon and Beckett - who has now scored three times in this year's
FA Cup following wins over Accrington and Grimsby in previous rounds - will take
the headlines, Ritchie was happy to spread the praise evenly across his side.
'We've had so many great performances out there that I couldn't single out
anyone.
'For our winning goal there was great movement. Schoey (Danny Schofield) has
put in a great ball, Luke was running the channel and pulled in a great ball and
we've been telling Chris to get to the back stick all season. He finally did and
it worked.
'But I can't single anyone out because they were all fantastic.'
For Birmingham boss Alex McLeish, in his first management role south of the
border, it was a grim introduction to the competition.
The former Rangers and Scotland boss admits he was desperate not to be on the
receiving end of a giant-killing and has called for his players to take a firm
look at their personal contributions to defeat.
'The Premier League is our priority and it remains our priority but we wanted
to win this match, no question,' said McLeish.
'I've been involved in cup upsets as a player and a manager. I've been a
giant killer but I've seen the other side and I didn't want to be a victim
today.
'The players will be embarrassed by it because they'll get bad headlines and
so will I. That is the position we are in.'
Reflecting on what had been said to his off-colour side behind closed doors,
he added: 'The dressing room chat remains private and that is where it must
stay.
'But every one of our players can look in the mirror and say 'we've let
ourselves down and let the fans down'.
'We had three or four internationals out there and we should be better than
that.'
Huddersfield Town 2 - 1 Birmingham
