Michael Gault says he was confident he would break Glentoran's heart when he stepped up to slot in the winning penalty at the Oval on Tuesday night.
The tense shootout success keeps the Blues on course to win a trophy they haven't grasped since 2008.
But they are still in with a shout of capturing the prize for the 30th time – any silverware this season would give the club a huge lift after a rare, trophyless campaign last time round.
Glentoran had defended with great courage, particularly after the dismissal of Mark Clarke 12 minutes after the break and it appeared written in the stars that the east-Belfast side would progress when their former hero, Andy Waterworth, missed the first penalty.
But John McGuigan and Jordan Hughes were also wayward from the spot, allowing Gault the chance to settle the marathon contest.
There was significant pressure on the Linfield talisman as he approached the goal in front of the travelling support but the midfielder produced the finish a clinical marksman would have been proud of.
"I had been hitting free-kicks and penalties in training quite well but I suppose I am not renowned for them," said Gault.
"I've always thought about hitting a big one and I felt the time was right to give it a go. I was quite confident because it was a nice situation to be in.
"If I scored we would win the game so there was a nice reward there.
"If I missed the penalty we would still have had another chance, but thankfully it went in.
"I thought about changing my mind and side footing it into a corner but I didn't and it worked. It was the right decision to stick with the original plan."
Gault admitted it was a frustrating night for the players and fans as neither side could conjure up the one bit of magic that might have produced a goal over more than 120 minutes of football.
"It was very frustrating for everyone including the supporters because they would have backed us to go on and win the game after the Glens were reduced to 10 men," admitted Gault.
"But the Oval is always a tough place to come to and it's about getting into the next round, which is what we achieved."
The outcome keeps Linfield spirits high going into Saturday's home league game with Dungannon Swifts. The Blues have now won their last eight games.
"It's about keeping the run going," added Gault. "Psychologically it's great for us and we are into the next round.
"We couldn't say the same last year when we were struggling.
"Our confidence is high after the way we have been performing in the league and we can look forward to Dungannon Swifts.
"They are a team that are performing very well as well so it will be another tough game. Hopefully we can get the three points."