Stephen Kenny's side cruised to victory over the China U-22 side with a brace from Adam Idah, both scored from the spot, and goals from Zach Elbouzedi & Aaron Connolly.
Ireland were ahead within 33 seconds and China's first touch of the ball was to pick it out of the net after Elbouzedi's brilliant finish. Ireland worked it neatly down the left and after fantastic work by Connolly, his low cross was left by Idah for the Waterford attacker, who finished off the bar.
It got even better for Ireland just seven minutes later. With their second attack of the game, Connor Ronan's free-kick was cleared but recycled back to Dara O'Shea and his header found Connolly to finish.
Ireland didn't have it all of their own way and China found a way back into the game as Li Yang headed home from a left-sided corner in the 18th minute.
After the break, Stephen Kenny's side were disciplined and ruthless, as they went on to score two more goals, both from the penalty spot. Ten minutes after the break, Elbouzedi's cross struck the arm of the defender and Idah stepped up to place his penalty into the bottom left-hand corner.
Ireland sealed the win and completed the scoring with ten minutes remaining. Once again, China were penalised for handball and Idah made no mistake from the spot to clinch his second goal of the game, and complete a fantastic victory.
"We're delighted to start the tournament with a win, it's huge credit to the players who have worked really hard since coming into camp on Tuesday," said U-21 boss Stephen Kenny.
"This Chinese team have had some good performances and we've watched them play very well, so the goals were at critical times for us and maybe made it look easier than it could have been.
"We've got great Irish players and we really want them to show the potential that they've got, their ability and I think we can take great encouragement from what we've seen today. We've got Mexico next and that will be a really tough match, but we can take a lot of confidence into Tuesday."
Republic of Ireland: Kelleher (GK), O'Connor, Leahy, Masterson, O'Shea, Coventry, Molumby (C) (Lennon 87), Ronan (Knight 62), Elbouzedi, Connolly (Power 77), Idah (Drinan 81).
China: Guo (GK), Wen (Guo 68), Li, Wu (C), Tong, Yao, Huang (Jiang 79), Lin, Shan, Chen, Lei.