Washington scored four goals in the first period and surged to their seventh straight win. Ovechkin's nine-game point streak was snapped, and the defenseman Green was held in check for the second straight game after going nine in a row with a point.
"They are in a groove," Capitals coach Bruce Boudreau said of his club. "A team, whether you are a first-place team or 30th, at some point of the season things seem just seem to be working and clicking. Right now, they are clicking for us. We had seven goals, and Ovie and Green didn't get a point. It shows you've got good balance."
Semin had two unassisted goals, and Brendan Morrison and Mike Knuble also scored against Dwayne Roloson in the first period for the NHL's most potent offense. Washington recorded only 12 shots in the frame but carried a 4-1 lead into the second.
Knuble's goal, scored during a power play just moments after Ovechkin struck Islanders defenseman Jack Hillen in the face with a shot, made it 3-1 with 1:47 left in the first. Semin pushed the advantage to three goals when he scored with 5.2 seconds left.
Roloson stopped eight of 12 shots before being replaced by Rick DiPietro to start the second. DiPietro allowed goals to defenseman John Erskine and Jason Chimera in the middle frame, and to Brooks Laich in the third.
"When we get [ahead] here, this team doesn't let up," Chimera said. "We just kind of keep on scoring goals and it makes it tough for teams to get back in it."
Washington, which leads the NHL at 3.81 goals per game, has scored at least four in 10 of the past 11 contests (10-1) -- a run that started the night Ovechkin was named Capitals captain. Eastern Conference-leading Washington (34-12-6) has the league's longest current winning streak.
"It was just a bad game all around," DiPietro said. "When we don't play our game, things like that happen."
The only negative for the Capitals was that their run of 14 straight penalty-kills was snapped.
Jose Theodore was the beneficiary of the offensive outburst. He lasted only two periods before being replaced by Michal Neuvirth to start the third. Theodore, who stopped 18 shots, is day to day because of a lower body injury, Boudreau said.
Morrison got things started 1:05 in when he deflected Erskine's shot past Roloson. Semin made it 2-0 just 3:44 later when he cut left-to-right in the Islanders zone and snapped a drive in on the Capitals' fourth shot.
Knuble and Semin connected in the final moments of the period to turn it into a rout.
"They are just a dynamic offensive team. You can't make any mistakes," Islanders coach Scott Gordon said.
The Islanders have dropped two straight at home following a six-game winning streak there. They have also lost three of four overall following four consecutive victories. Roloson has given up at least four goals in three of his past five outings since DiPietro returned from injury.
"Mentally, I didn't want him to get beat up," Gordon said. "The way they were scoring, I just felt it was an opportunity to get Rick in there and not have it all come down on [Roloson]."
Erskine ended a 109-game scoring drought, dating to Jan. 19, 2008, at 2:36 of the second -- giving the Capitals three goals on five shots spanning the first two periods.
"I don't get them too often, so I wasn't even sure what to do when it went in," Erskine said.
Chimera answered Okposo's goal to make it 6-2 at 13:58. That virtually assured these teams would not go to overtime as they had done in four straight games on Long Island and seven of 10 overall. Washington is 7-0-1 in its past eight against the Islanders -- including 3-0-1 in the completed season series.
Hillen was taken to the hospital for evaluation after being bloodied by Ovechkin's shot to the chin. ... The Capitals' season high is eight goals. They have netted at least five in 16 of 52 games. ... Semin became the fourth Capitals player to reach 50 points this season. ... Islanders 18-year old prospect D Calvin de Haan will have shoulder surgery on Thursday and be sidelined six months, the team said.