Garry Thompson put the League Two outfit ahead in the 16th minute when he volleyed past Wojciech Szczęsny before Vermaelen levelled with just two minutes remaining.
With Jack Wilshere spurning the best chance of extra-time, Arsenal trio Santi Cazorla, Marouane Chamakh and Vermaelen all missed spot-kicks to see Bradford progress.
Here is the best of the Twitter reaction from the professionals.
Former Tottenham chairman Lord Sugar (@Lord_Sugar) is envisaging the excuses after Arsenal lose: “Bradford score against Arsenal in a Cup game. Wenger will say we are giving the kids a run out.”
Ex-Gunners midfielder Ray Parlour (@RealRomfordPele) can’t believe what is happening: “Oh No!!”
Former Liverpool midfielder Neil Mellor (@NeilMellor33) suggests Bradford have scored too early: “Could be a major shock if Bradford win this!!! An early goal! Too early?? Long way left but great start versus Arsenal!”
Bolton midfielder Fabrice Muamba (@fmuamba) loves football’s upsets: “OMG Bradford City one up against Arsenal. Football is full of surprises!”
Celebrity Arsenal fan Piers Morgan (@piersmorgan)is unhappy at Aaron Ramsey’s lacklustre display: “So Ramsey cocked it up again? His continued presence in Arsenal’s first team is yet another reason why I say Wenger’s lost it. #Arsenal”
Southampton’s Richard Chaplow (@Rchap04) thinks if haircuts are any indication: “I’ve got to say if I did have hair, I’d have it nothing like Chamakhs! #terriblebarnet #notjealous #talktome”
Swansea defender Kyle Bartley (@kylebartley22) is shocked Arsenal are behind with little time left: “What is going on with Arsenal?! #WOW!”
Former England legend Gary Lineker (@GaryLineker) reckons Morgan is overrating Chamakh: “RT @piersmorgan: Chamakh is absolutely USELESS. #Arsenal < That good??” Ex-Wimbledon start Jason Euell (@jasoneuell) tweets as the drama unfolds: “Before the game, pundits, media and commentators were saying it is a strong #AFC team. I’m hoping they turn up with five minutes to go… There you go. Turned up 86th minute… #afc!”
Former England cricket captain Michael Vaughan (@MichaelVaughan) refers to a previous incident involving Andre Santos at Old Trafford: “I wonder if the Arsenal players will want to swap shirts with the Bradford players before the shoot out @piersmorgan!”
Arsenal midfielder Emmanuel Frimpong (@Frimpong26AFC) is clearly frustrated: “Leave it.”
Former Crystal Palace striker Mark Bright (@Mark__Bright) is pleased for the League Two outfit: “Well done Bradford City thoroughly deserved…. Epic Victory #afc!
Finally, West Brom midfielder Steven Reid (@stevenreid12) enjoyed all the drama: “Congratulations Bradford enjoyed that shoot out immensely!”
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