Nathan Walker, debuting as the first Australian to play in an NHL game, scored with 1:55 remaining for a 6-1 lead.
"I'm at a loss for words," Walker said. "That's incredible. A really special moment, a proud moment."
Ovechkin (at 20 seconds) and T.J. Oshie scored in the first 46 seconds for a 2-0 lead. Ovechkin scored a power-play goal at 2:51 to make it 3-0, and gave the Capitals a 4-0 lead with 1:50 left in the period. He made it 5-1 with 3:14 left in the second period.
"You give him an inch, that's all he needs to snap it home," said Montreal defenseman Karl Alzner, Ovechkin's teammate for nine seasons in Washington. "On the first one, an inch. On the tip-in, an inch. And that's it. Sometimes you play good [defense] and it just doesn't work out. That's what good players do."
Canadiens goalie Carey Price made 10 saves. He was pulled and replaced by Al Montoya to start the second period. Brendan Gallagher scored a shorthanded goal for Montreal 4:50 into the second.