Frank Vaesavali Tato bagged a hat-trick as the Baby Manu outclassed Hong Kong 41-20 in the opening match of the tournament in Bucharest.
Samoa were relegated from last year's Under 20 Championship but have a perfect record in the second tier competition, having won the event in their two previous appearances in 2011 and 2016.
Meanwhile the Baby Flying Fijians overcame two yellow cards to defeat Uruguay 55-34.
