"They can be scary," Toronto coach Ron Wilson said of Capitals' offense.
It was the second straight dominating offense performance by Washington. The Capitals posted a convincing 4-1 win over Boston on Thursday night as Ovechkin scored two goals and added an assist. Semin contributed two assists.
"You know the Alexes are going to score," Washington coach Bruce Boudreau said. "We'll get other guys to chip in every now and again. We'll score our three or four goals a game."
It was Ovechkin who scored first versus the Maple Leafs. Only 77 seconds into the first period, Ovechkin beat Vesa Toskala on a low rocket shot.
Toronto defenseman Mike Komisarek took his sixth penalty of the season when he tripped Brooks Laich with 12:33 remaining in the first period.
Washington took advantage. Mike Knuble, the Capitals marquee free-agent signing of the off-season, knocked in Ovechkin's rebound on a shot from the point right in front.
Laich made it 3-0 late in the period, scoring on a breakaway.
Russian goalie Semyon Varlamov, making his first start of the season, looked sharp early, making 10 saves, including two nifty ones midway through the period. He stopped a point-blank attempt from Viktor Stalberg and stretched out to stone John Mitchell as he tried to wrap it around from behind the goal.
"I thought for the first two periods he was great," Boudreau said. "When he had to make the big save, he made the big save. Then, I think the guys in front of him let him down in the third period."
After the first period, Toronto coach Ron Wilson pulled Toskala, who gave up three goals on only eight shots, and replaced him with Jonas Gustavsson.
Gustavsson didn't fare much better, yielding three goals on 12 shots with Washington jumping out to a commanding lead 6-1 lead.
The goaltending left Toronto coach Ron Wilson frustrated. He isn't sure who will be his starter when the Maple Leaps host Ottawa Tuesday.
"We will watch the tape and I don't have to make a decision tonight," Wilson said. "We will decide on Monday who is going to start. We score one and then, boom, boom, boom. Three more goals. I am not saying it's Jonas' fault. I am sure it was good experience for him to see us play against maybe the best offense team in a tough environment."
Semin scored twice on Gustavsson, flipping the puck over a sprawled goaltender early in the period.
Then, with 3:58 left, Semin lost control of the puck, but it went off defenseman Francois Beauchemin and in.
In between Semin's goals, Brendan Morrison scored on a breakaway.
The Maple Leafs played with more intensity in the second period, but Varlamov stopped seven shots in a four-minute stretch before Lee Stempniak trimmed the lead to 3-1.
Alexei Ponikarovsky, Mikhail Grabovski and Niklas Hagman finished Toronto's scoring in the third period.
Boudreau didn't like the Capitals' breakdowns in the final period after five strong periods to start the season.
"Our first five periods were pretty good," the coach said. "Anytime you win, you shouldn't complain. I told the guys it was a great win and great start, but we have to learn how to win 6-1 when we were in that position and not think we are going to win 9-1. Hopefully, it was a cheap lesson for us and we can (be) successful from it."
Notes: Defenseman Garnet Exelby and forwards Jay Rosehill and Nikolai Kulemin were healthy scratches for Toronto. Defensemen Jeff Schultz and Tyler Sloan and center Michael Nylander sat out for Washington.
--Tom Worgo, NHL.com Correspondent
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