Wahlstrom gave the Islanders a 1-0 lead when his shot deflected off Capitals defenseman Trevor van Riemsdyk at 9:50 of the first period, and Casey Cizikas redirected a shot from Cal Clutterbuck at 10:08 to make it 2-0.
Anders Lee gave New York a 3-0 lead when he scored on a rebound at 17:39, but Vanecek shut out the Islanders the rest of the way.
"We had a great start; we got to our game right away and did what we wanted to do in that first period," said Lee, the Islanders captain. "Obviously, the second period we had a pretty bad lapse and that's what turned the game around completely. At the same time, we're looking at it as plenty of hockey to get ourselves back into it, similar to how they clawed themselves back. We just weren't able to find the first one to get us going, and it turns into a bad loss."
Tom Wilson, who returned after missing two games because of a lower-body injury, scored an empty-net goal on the Capitals' only shot of the third period at 19:41 for the 6-3 final.
NOTES: Forward Josh Bailey played his 872nd NHL game, all with the Islanders, which tied him with forward Clark Gillies for fourth on their list. … Lee played his 500th NHL game, also all with New York. … Each of the Capitals' past three five-goal periods have been against the Islanders (Jan. 18, 2020 and Nov. 5, 2013). … Schultz, who has scored multiple points in three straight games (two goals, four assists), left in the third period after getting hit in the face by a shot from Islanders forward Kieffer Bellows. Laviolette said Schultz was being evaluated.