Alex Ovechkin scored twice in a 1:27 span early in the second period and Braden Holtby stopped 20 shots for the Capitals to get his league-leading 36th win of the season. The Capitals beat the Islanders for the third time in three meetings this season and ninth in the last 12 (9-1-2).
Washington, which leads the NHL with 88 points, won for the fifth time in six games and improved to 15-3-2 against Metropolitan Division teams.
John Tavares and Frans Nielsen scored goals and Thomas Greiss had 32 saves for the Islanders, who had won four of their previous five. New York snapped a four-game home winning streak and will play 12 of its next 14 on the road.
Nielsen tied it with 1:44 left as Travis Hamonic sent the puck toward the goal from the blue line and after it settled about a foot from the goal line, Nielsen tucked it inside the right post.
Ovechkin hit the post with a shot 1:07 into the 3-on-3 overtime and had a slap shot stopped by Greiss 30 seconds later.
With the Capitals trailing 1-0 after one period, Ovechkin tied it 1:25 into the second. Evgeny Kuznetsov skated with the puck behind the net, turned and passed back to Ovechkin at the right side of the net and he fired it past Greiss. Kuznetsov got his 42nd assist and 58th point — both team highs — on the play.
Nearly 35 seconds after the Islanders' Cal Clutterbuck was whistled for boarding the Capitals' Dmitry Orlov, Ovechkin gave Washington the lead at 2:52 with his league-leading 37th goal of the season. Nicklas Backstrom took a pass from T.J. Oshie as he crossed the blue line and dropped the puck back to the left for Ovechkin, who fired it past Greiss.
Ovechkin increased his total to 30 goals in 40 career games against the Islanders and helped the Capitals improve to 32-0-1 when leading after two periods.
New York's Thomas Hickey and Washington's Tom Wilson were called for coincidental penalties for boarding each other 31/2 minutes into the second period and continued yelling at each other for several minutes while sitting in their respective penalty boxes.
With Ryan Strome off for elbowing, Greiss was whistled for delay of game near the midpoint of the period to give Washington a 5-on-3 advantage for 58 seconds. However, Greiss stopped both Capitals shots in that stretch.
Washington outshot New York 14-4 in the second period and 35-22 for the game.
The Islanders dominated the play early, outshooting the Capitals 6-0 before Greiss stopped a wrist shot by Oshie 6:15 into the game.
Tavares got New York on the scoreboard first with his team-leading 22nd goal. He took a pass from Nick Leddy, skated through the right circle and got past defenseman Nate Schmidt, went backhand to forehand and wristed the puck past Holtby with 4:19 remaining in the first period. It was the Islanders captain's seventh straight game with at least a point and gave him seven goals and nine assists in his last 11 games.
NOTES: Washington snapped a 20-game streak of scoring in the third period. The Capitals have outscored opponents 72-46 in third periods. … C Mike Richards has no points in 13 games since joining the Capitals as a free agent last month. … Oshie appeared in his 499th career game. … The Islanders were without D Calvin de Haan, who missed his first game of the season due to a lower-body injury sustained in Monday's win over Detroit. Brian Strait played in his place. … Greiss played in his career-high 26th game. His previous high was 25 with Phoenix in 2013-14. … Leddy's assist on Tavares' goal in the first period gave him a point in four straight games. He has nine points (one goal, eight assists) in his last nine games.