Alex McLeish paid tribute to golden oldies Kevin Phillips and Maik Taylor for rescuing Birmingham from Carling Cup humiliation and securing a quarter-final spot.
Blues looked on their way out of the competition when they trailed at home to npower League One side Brentford who had knocked out Everton in the previous round.
But 37-year-old Phillips cancelled out Sam Wood's goal in the second minute of injury time and then Taylor, 38, saved Craig Woodman's spot-kick to seal a 4-3 penalty shoot-out win.
McLeish said: "It was not about loyalty as such when we gave them new contracts in the summer.
"In this game as a manager, at times you have to be quite ruthless.
"But we felt there was still mileage in these two guys and you saw in this cup tie that there certainly is.
"Kevin will never lose that knack in the danger area, his ability, his touch, his awareness.
"He is a classy guy and he despatched his penalty as well in the shoot-out.
"He probably feels he has not got the real sharpness because he has not been featuring much but Kevin is a guy we know, if we bring him in, will produce something."
McLeish added: "Maik is also a top pro and I think some advice from Dave Watson (goalkeeping coach) helped with the last penalty.
"He said the chap who took the last penalty (Woodman) tended to hit it straight down the middle and Maik stood his ground and saved it.
"It was some good information and this is why research is very important."
McLeish admitted: "Brentford were excellent, superbly organised and I thought we were out of the cup.
"But the never-say-die resilience of the team came to the fore again.
"When you've got the hunger and desire to go right to the end, then you can never say that you are finished until that final whistle."
Brentford manager Andy Scott took pride from his side's performance.
He said: "We gave them some real problems and just couldn't hold out long enough unfortunately.
"We've won a lot of friends with the cup run. We've brought 3,000 fans to Birmingham and showed we've got a strong club.
"We've got belief in each other and quite a lot of ability as well.
"We've been galvanised by our cup run and have taken it into the league.
"We held on against Everton and performed brilliantly tonight for 120 minutes.
"You can't fault the lads. They restricted a good Premier League side to very few chances and we had several more than that."