Birmingham head coach Pep Clotet praised the workrate of his team after they twice came from behind then beat Coventry 4-1 on penalties after the Emirates FA Cup fourth-round replay ended 2-2 after extra-time.
Goalkeeper Lee Camp saved penalties from substitutes Liam Walsh and Jamie Allen as Birmingham won the shootout to clinch a fifth-round tie away to Leicester.
Harlee Dean – in the second minute of time added on – and Jeremie Bela, in the 120th minute, equalised to send the game to a shootout after finishing 2-2 with Amadou Bakayoko (50) and Jamie Allen (114) twice putting the Sky Blues ahead.
"Coventry made it very difficult for us and we struggled to create flow in attack but one thing we had was the ability to work harder to the end, believe in ourselves and take the game to a penalty shootout," said Clotet.
"We are very happy it went in our favour. It was a fantastic night.
"It turned out well after eight years of us not being able to get into the fifth round but we managed it. All our fans will be very excited.
"We saw a fantastic cup game. The levels do not matter whether it's Premier League, Championship, Leagues One or Two."
Clotet revealed Birmingham had done their homework on Coventry's penalty taking for the possibility of a shootout.
"We analysed all of Coventry's penalties this season so we knew where their players tend to shoot and all of the information was given to Lee Camp, but he still had to make his decision," said Clotet.
Coventry manager Mark Robins felt his side deserved to have gone through before the shootout.
"We looked like we were going to be fairly comfortable winners – we had chances at 1-0 and 2-1," said Robins. "We had three chances to have won it before they equalised.
"To concede within three minutes of extra-time was poor and we have to learn our lessons from that.
"We can talk about disappointment but there's immense pride.
"They (Birmingham) deserved to go through based on penalties but not based on the 90 minutes and extra-time.
"We scored two brilliant goals – the second one was outstanding – but the frustration was we didn't take our chances, and our chances were clear cut."
Coventry lost the toss to decide which end was being used for the shootout – the stand (Tilton End) was empty – only for Birmingham fans to rush round and start filling up the seats to try to give their team an edge.
"Obviously it made it difficult because they made the difference when they were kicking into an empty stand," said Clotet.
Robins had no complaints, saying: "It's a lottery either way. We lost the toss and it is what it is.
"Lee Camp made two really good saves and their lads stuck their penalties away really well."
Dean's spot kick sealed victory, while substitutes Lukas Jutkiewicz, Bela and Gary Gardner also netted from the spot.
Dean made it 1-1 in the second minute of time added on, and a hopeful cross by Bela in the 120th minute saw Birmingham draw to cancel out goals from Amadou Bakayoko (50) and Max Biamou (114).
Biamou missed two excellent chances at 1-0 to have given the League One side a two-goal cushion.
