Mackay Mackay said: ''We've already been in extra-time in this competition twice this season so I'm delighted to get through again.
''The technique of the penalties was fantastic and it's great to beat an experienced team and manager in front of our own fans. It's a special win.
''I was delighted with the way the team applied themselves. They showed togetherness and it made the difference.
''It's great to have players who have individual talents, but you need players who run hard, cover for each other and are honest. It makes for a good dressing room.''
In normal time, Steve Howard and Lloyd Dyer scored for Leicester while Don Cowie and Rudy Gestede netted for the hosts to set up an extra half-hour.
The additional time could not separate the sides and the contest continued to be equal for the first 12 penalties before Fernandes eventually missed.
But Leicester boss Sven-Goran Eriksson refused to blame the former Manchester City midfielder for his miss.
Eriksson said: ''Penalties are not Gelson's business. When you get to the seventh taker and you have already used your three substitutes then you are coming to those players who normally don't take them.
''He will have forgotten about the penalty in the next 24 hours. I have lost many penalty shoot-outs before in my managerial career and it's a pity to lose.
''We did make a lot of changes, but I felt we were the better team and would go through.
''It was a good performance from the players who came in and they should all be proud of their display.''
Eriksson made 10 changes for the third-round tie at the Cardiff City Stadium, but the Swede claimed he would not change his selection thought process if he had another chance.
Eriksson added: ''I hope the competition is not devalued. It is an important cup, but if you looked at the line-ups of the other games, there are a lot of changes.
''We have 46 games to play in the league, without the FA Cup, and you need a big squad to do that.
''Sometimes you need to give the players in your squad the chance to play. I would do exactly the same again if we played the game tomorrow.
''We have the ambition to have a big squad and we may need those players further down the line.''