The 34-6 success was his first game at senior level and the 17-year-old received a remarkable ovation from the 9,000 crowd when he came off the bench with around 15 minutes remaining - and again after converting a try moments later.
Sinfield’s surname means he will be under more pressure than most young players, but coach Richard Agar was pleased with how the scrum-half handled the occasion, six years after his father Kevin made the last of his 521 appearances for Rhinos.
“It was great, I really enjoyed it,” Jack Sinfield said of the Wetherby Whaler Festive Challenge.
“I had an idea [he was going to play] last week, but only knew for definite on the 23rd.
“It was good to get on, I loved it.”
Sinfield was the only member of Rhinos’ 20-man Boxing Day side without a competitive first team appearance.
His father captained Leeds to seven Grand Final wins and is the club’s record goals (1,831) and points (3,967) scorer. The reception Jack received reflected what the Sinfield name means to Rhinos and he said: “It was really nice.
“It made me feel more comfortable and confident, so it was good.
“I was really nervous before the game, but the longer it went on [while he was on the bench], the better it got and I was all right when I went on.”
Sinfield’s debut training session with the first team squad was at Headingley on November 23, the day Kevin completed his 101-mile charity run from Leicester to Leeds.
“I feel like I am learning and getting better.
“They have all been great with me, giving me little tips and pointers.
“I am enjoying learning from people like that.”
Of his hopes for a possible Betfred Super League debut in 2022 - Sinfield added: “Fingers crossed.
“I just want to keep getting better for now, keep improving and just see where I end up.”
Sinfield signed a professional contract in August, a week after Kevin left his role as Rhinos’ director of rugby to become an assistant coach at union giants Leicester Tigers.
After impressing in Rhinos’ under-16s and 17s, Jack had interest from other clubs in both codes, but insisted: “I have always been a fan, so it was always going to be Leeds.
“It is a bit crazy, to be honest, but I am loving it, it is really good.
“The young lads have helped me settle in because I knew most of them before I moved up and the older lads have all been great with me, really welcoming.
“They have made me feel part of the team. Hopefully I can keep pushing in training and get a few more minutes [in pre-season matches].
“The more I play, the more comfortable I’ll get and hopefully the more I’ll progress.”
Tigers had a game on Boxing Day so Kevin Sinfield was not at Headingley to see his eldest son’s appearance.
Of whether the former England captain had passed on any pre-match tips, Jack stressed: “He just wants me to enjoy it and just make sure I am working hard - that’s all really.”