Sheyi Ojo, Max Woltman and Melkamu Frauendorf were also on the mark for Barry Lewtas' side.
Lewtas told Liverpoolfc.com: "It was another good outing from the boys and we played some really nice stuff. I was pleased for Fidel to get his hat-trick and that will be brilliant for his confidence.
"Fair play to Caernarfon, they tried to play the right way and I wish them all the best for the new season."
The young Reds opened the scoring after just seven minutes when O'Rourke produced a stunning finish into the top corner from distance.
Ojo then doubled the lead with a close-range header after Tom Clayton's rasping drive was saved.