Valtteri Filppula scored twice for New York (48-27-7) after missing seven games because of a hyperextended elbow, and Robin Lehner made 29 saves for his sixth shutout of the season.
The Islanders, who finished the regular season by winning six of their last eight games, will have home-ice advantage in the Eastern Conference First Round of the Stanley Cup Playoffs against the Pittsburgh Penguins, who finished third in the Metropolitan.
WATCH: [All Islanders vs. Capitals highlights]
It's the first time New York will have home-ice advantage in a playoff series since 1988.
"We really wanted home ice," Lehner said. "We've seen how special the [Nassau] Coliseum's been and all the fans and it's going to be a really fun series. They're a good team. It's going to be a good challenge. If we stick to our game, I like our chances."
Lehner and Thomas Greiss will share the William M. Jennings Trophy for the Islanders, who allowed the fewest goals (191) in the NHL after giving up a League-high 293 last season.
"It's a team award," New York coach Barry Trotz said. "But it starts in the pipes between [Greiss] and Robin giving us consistent goaltending for the most part all year, making big saves at key times. And then the rest, in terms of structure, work ethic and commitment, everybody else contributed to that."