The 20-year-old - starting in the No.13 jersey - made an immediate impact with a sharp break to set up Isa Nacewa's try after just three minutes.
That laid the foundations for an eye-catching display in Limerick and Cullen admits Ringrose has all the tools at his disposal to rise to the very top.
"I think Garry did a lot of really good things," Cullen told the The42.ie
"It's trying to keep giving him those positive experiences and I think Garry is going to be a great player. We hope he's going to be a great player.
"He's someone who works incredibly hard, and that's the most important part, that he has that gradual improvement all the time.
"He puts in the work every day and you see out there that he gets the rewards. It's really pleasing and I think that's a really important lesson for anyone playing the game; it comes down to the preparation you put in day after day.
"He's someone who really epitomises that."
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