Mathew Barzal scored, and Semyon Varlamov made 39 saves for the Islanders, the No. 4 seed.
Teams that win Game 3 are 366-156 (65.5 percent) winning a best-of-7 NHL playoff series after it is tied 1-1, including 4-2 last season. Game 4 is here Saturday (7:15 p.m. ET; NBC, CBC, SN, TVAS).
"I've got to watch the replay," Varlamov said. "We just finished the game. I didn't even see the replay. So I've got to kind of go back in the locker room and I don't really have an answer for you right now. It was kind of a weird shot, but the puck found the net. So, it was a good play, I guess, by Marchand."
Barzal tied it 1-1 with 5:26 remaining in the third period when he got to a rebound off the end boards and jammed the puck in at the left post for his first goal of the playoffs.
Barzal had a chance to win it in overtime, but Rask made a pad save on his rebound attempt at 2:08.
"Tuukka made a great save," Barzal said. "Usually in those situations, I thought I was in tight and just wanted to sneak one five-hole, but he was there. He was big all night for them as was 'Varly.' So it's unfortunate."