The striker scored from the spot deep in added time on Tuesday to send the Greeks through to the last 16 and dump their opponents out of the tournament.
Despite so much riding on the penalty, Samaras insists that he felt calm when he stepped up to take it.
"What did I feel at that moment in time? Nothing at all," he told FIFA.com. "I just took the ball and placed it on the spot – me against the keeper. My mind was clear. I kept my focus and just tried to put it in the back of the net.
"I've done it thousands of times in training and a few times in matches. If you think about it, it makes no difference if there's one person watching you at your club or thousands in a stadium."
Greece will now face Costa Rica on Sunday for a place in the quarter-finals.