The 18-year-old winger was introduced by manager Chris Hughton with his side 2-0 behind and staring at Capital One Cup elimination.
But Murphy rifled in a 76th-minute strike to give the Barclays Premier League side hope before Hooper levelled with the last touch of normal time at Vicarage Road.
The visitors then secured their spot in the fourth round when Hooper slotted home his second in extra-time to seal a memorable 3-2 win, with Murphy delighted with his own first-team bow.
"[It was] Unbelievable, it was the best moment, just surreal," he said.
"I picked the ball up and just hit it, I just thought I'd see where it goes and luckily it hit off the bar and went in.
"I wanted to go and celebrate with the fans because they were unbelievable tonight but obviously we were 2-1 down so we just got the ball straight back."
Hughton had suggested Murphy would be involved at some point and even admitted he had considered starting one of the men who starred in the Canaries' youth cup win last season.
Murphy said he was told to go out and play his own game but still felt responsibility to help his more experienced team-mates turn the game on it's head.
"He [Hughton] told me to just go on and do my thing and see what you can get out of the game," Murphy added.
"I would have savoured the moment anyway but then I saw their right-back was vulnerable and cramping up.
"Just because I'm the youngest doesn't mean I'm any different to the other players, everyone went out there and did their jobs, stuck to the task and we ground it out."
Watford had scored two well-taken goals to put Gianfranco Zola's side on the brink of the fourth round.
Davide Faraoni's stunner seven minutes in to the second half had the hosts on course for a minor upsets after Javier Acuna had opened his account for the Hornets by arrowing in an effort midway through the first half.
On a night of firsts the former Real Madrid man revealed he was pleased to notch his maiden goal for Watford.
"It's my first goal for Watford, and I'm very, very happy," he said.
"[Diego] Fabbrini gave me the ball, I turned, saw the goal and hit the ball as hard as I could.
"The ball went left and right in the air, and luckily it went in. I'm very happy for my first goal at Watford and I hope to score many more."
The 25-year-old Paraguayan also felt that Zola's side were unlucky not to progress in to the final 16.
"It was such a shame to concede with just 10 seconds left," he said.
"We played well and we deserved more. We need to continue improving."