The former Caerleon Comprehensive pupil was promoted from the bench to the starting XV for the 20-10 loss to the Ospreys after Pat Leach's late withdrawal with a virus.
Morgan played alongside fellow teenager Jack Dixon against Wales international pairing Ashley Beck and Jonathan Spratt, more than holding their own in the Judgement Day fixture.
And the youngster, who played on the wing for Wales Under-20s during the Six Nations, also played a vital role in scrum-half Richie Rees' try.
"It was a great place to make my league debut," said Morgan, who heads to New Zealand with Wales this summer for the Junior World Championships.
"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."
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