The Saints skipper, a former youth player at Celtic, inspired his side to victory over the Parkhead side yesterday at Hampden.
And to his great relief, he learned that he will be eligible to lead the Buddies out for the final against Hearts, despite picking up a booking after conceding a penalty for hand ball.
Goodwin is adamant that Saints deserve all the credit for staying true to their passing ethos rather than trying to sit in and stifle Celts.
With Saints having lost all previous eight meetings with the Glasgow giants under Danny Lennon, and having conceded 22 goals without reply in the process, they entered the semi-final as massive underdogs.
But gaffer Lennon sent his men out to take the game to Celts and handed a debut to new Portuguese loan signing Esmael Goncalves, who scored Saints' opener.
At the other end of the park, Goodwin was the defensive lynchpin in a resolute Paisley backline, and his partnership with Marc McAusland was crucial in repelling the Hoops.
The St Mirren skipper said: "This is without doubt the proudest moment in my career. To lead St Mirren out at Hampden was huge for me, but to captain the side to victory over Celtic in a semi-final is just unbelievable.
"I have won a championship with Scunthorpe, but this beats that big time. Obviously I was at Celtic as a kid and to be leading out St Mirren against them in the semi at Hampden, which was the first time I had played here, was immense.
"But to get the win is just incredible and I just hope we get the credit for it rather than people saying that Celtic did not turn up.
"We stayed true to the way we try and play the passing game and I thought we were the better side from start to finish. I think we deserved this win and we played the better football."
Goodwin admits his harsh booking for handball in the incident that led to Celtic's penalty, which was saved by Craig Samson, had left his heart in his mouth over his eligibility for the final against the Jambos.
He said: "It was a worry for me, but as I left the pitch I was told I was still eligible and I think the person said I only had two yellow cards and it is three that would have banned me.
"So I was very relieved to hear it and felt like I could breathe again. To have played a part in such a huge win and then not been available to see the job through in the final would have been heartbreaking. But now we have made the final against Hearts we need to make sure we maintain the standard we produced against Celtic.
"We have made the final the hard way by beating the best team in Scotland, though, and that does give us huge self-belief."
Model pro Goodwin also had words of praise for teenage midfielder John McGinn, whose grandfather Jack was once chairman of Celtic.
He said: "It was a huge match for young John to play in, but he did not let the occasion get to him. To be in that midfield battle against the likes of Scott Brown and turn in that level of performance was immense from John.
"The level of belief he can gain from that experience will stand him in good stead going forward. But this was all about a collective effort.
"No one gave us a prayer going into this but we had a game plan, we stuck to it and we got our rewards and the gaffer deserves big credit for that."