The former Caerleon Comprehensive pupil was meant to be among the replacements only for Pat Leach's late withdrawal with a virus to lead to a promotion.
He slotted in alongside fellow teenager Jack Dixon to lock horns with Wales internationals Ashley Beck and Jonathan Spratt and the young pair did admirably.
Morgan who recently signed for the Newport Gwent Dragons for next season played a key role in scrum-half Richie Rees' try.
He played on the wing for Wales Under-20s during the Six Nations and is set to be a member of the squad that heads to New Zealand for the Junior World Championship this summer.
"It was a great place to make my league debut," he said. "When I was running out through the tunnel I was expecting a big crowd but when I came out I thought 'Jesus!' and froze for a second before focusing.
"It was a great atmosphere and the best I had ever played in. I had been training all week and knew I was going to be in the squad but thought I was going to be on the bench.
"But we found out the day before Pat Leach was not very well and it was 50/50 whether he would be ok. Unfortunately he was unwell but I was lucky to have the opportunity to start."
