Mantha, the QMJHL's leading scorer with 24 goals in 23 games for the Val d'Or Foreurs, broke a 2-2 tie at 15:53 of the third period.
The QMJHL's top line of Mantha, Hudon, and Jonathan Drouin, accounted for all the team's offence.
Drouin — the Halifax Mooseheads' winger who was selected third overall by the Tampa Bay Lightning in this year's NHL Draft — assisted on all three goals. Hudon picked up an assist to finish the night with three points, and Mantha, a 2013 first-round pick of the Detroit Red Wings, added an assist for a two-point performance.
Ivan Barbashev of the Moncton Wildcats and Vladimir Tkachev scored for Russia (0-1-0).
Hudon, of the Chicoutimi Sagueneens, opened the scoring at 11:56 of the first period. The Canadiens prospect added another at 4:02 of the second to give the QMJHL a 2-0 advantage.
Barbashev replied for Russia halfway through the second period to cut the deficit in half, and Tkachev tied the game at 6:06 of the third period, weaving through QMJHL's defenders before firing the puck into the net.
Zachary Fucale of the Mooseheads made 19 saves for the QMJHL (1-0-0). His Russian counterpart Ivan Nalimov stopped 21 shots in the losing effort.
Russia was 0-for-5 with the man advantage while the QMJHL was scoreless in six power-play opportunities.
Game 2 of the series is Wednesday night in Sherbrooke, Que.