Roy emerged as the wrecker-in-chief for India as he run through the opposition, returning with impressive figures of 6.5-2-14-5 after skipper Shaw won the toss and elected to field first under overcast conditions.
India then returned to overhaul the target, reaching 67 for no loss in 8 overs, riding on Shaw's 39-ball 57 which was studded with 12 boundaries.
It was Shaw's second half-century of the tournament, while Roy picked his maiden five-wicket haul in youth ODIs.
In conditions that aided swing and bounce, India fast bowler Shivam Mavi picked up two wickets, while Kamlesh Nagarkoti and Arshdeep Singh snapped one wicket each.
India will take on Zimbabwe next on January 19.
Papua New Guinea Under-19s: 64 allout in 21.5 overs (OL Sam 15; AS Roy 5/14)
India: 67 in 8 overs (PP Shaw 57; L MOrea 0/11).