At 11am that morning, Josh learnt that he would be in the starting line-up at Carrow Road, and celebrated the news by telling team-mate and twin, Jacob.
"Me and my brother went in the toilets and gave each other a high five," said Josh. "It was a big moment for us."
Josh enjoyed another big moment later in the day when he assisted Robert Snodgrass to head home the equaliser for the Canaries, following Darren Bent's goal in the 40th minute.
Despite a pleasing performance, the 18-year-old admits he was nervous as to what sort of welcome he was going to receive from the fans.
"It was my first start and you don't know how the fans are going to react to you. I just went out there and did what I could do best," he added.
"Some things didn't come off and I had to work hard to get the ball back. But some things did, which the fans appreciated."
The midfielder, who along with brother Jacob was a star player of Norwich's FA Youth Cup-winning squad last season, says he is aware that playing at a professional level means he has to up the ante.
"I'm not playing against kids any more, I'm playing against men," he said. "So it's going to be hard physically and mentally."
In the 78th minute, Josh was replaced by identical twin Jacob. This was Jacob's first-team debut, and a special moment for both brothers.
Josh explained: "I saw him getting undressed so I knew I was coming off. And when I saw him standing there with a little smile on his face, I thought 'it's your turn now'.
"Obviously I wanted to stay on longer, but just to see my brother come on to make his debut was unbelievable because he's worked so hard. It was a great night for the Murphys.
"We're there to support each other and when I came off, I was happy he was coming on because I know what he's capable of and all the backroom staff know what he's capable of.
"I was just happy for him to play. There is no rivalry at all."
Speaking of the impending replay against Fulham at Craven Cottage on January 14, Murphy says he is just relieved the Canaries didn't get knocked out of the cup.
"All the lads are happy to be in there and we've just got to go to Craven Cottage and get the result," said Josh.
"It was unbelievable to start. You could see I had a smile on my face all throughout the game and it was just a brilliant feeling.
"The replay isn't ideal because we have had all these games recently but I'd be looking forward to any game. If I'm involved, I will be there ready, have my boots and pads, and be raring to go."