Brad Boyes netted the game-winning goal in 3, at Nassau Coliseum.
Boyes picked up the puck and moved in slowly on Isles netminder Al Montoya. Boyes waited for Montoya to make a move and fired a quick wrist shot past the glove side of the Montoya. Jason Pominville sealed the victory with a goal in the second round of the shootout, while Ryan Miller stopped attempts from P.A. Parenteau and Frans Nielsen.
"Our defense was in really good position tonight," Miller said. "We made it hard for them to get the looks they wanted. "We blocked a few shots and I was able to get an eye on a few of them."
Nielsen finished with two goals and an assist and Josh Bailey also scored for the Islanders, who had their brief two-game winning streak halted. Montoya stopped 34-of-37 shots.
Trailing 3-1, Buffalo got within one at 18:41 of the second period when Ville Leino picked up the puck in the neutral zone and raced up the left wing. Leino slowed at the circle and dropped it off to Roy, who slapped it past a screened Montoya.
After carrying the play for much of the third period, the hard work paid off from the Sabres at the 11:46 mark when the puck came back to Tyler Myers at the right point and he found Gaustad open in the slot. The rugged center fired it past Montoya to tie the contest at three.
New York had a glorious chance to win it in overtime when the Sabres were whistled for a too many men penalty at 2:28.
The Islanders turned the final minutes of the period into a shooting gallery and spent nearly their entire power play in the offensive zone, but Miller came up with several huge stops to send the game to the shootout.
The Islanders wasted no time taking the lead, as Nielsen found the back of the net just 1:39 into the game after Michael Grabner chased down a loose puck behind the net and found Nielsen, who one-timed it past the blocker side of Miller.
Buffalo answered at 5:32 of the period when Drew Stafford chipped the puck ahead, sending Gerbe into the zone and the crafty forward let a wrist shot go that hit off Montoya, popped up in the air and landed across the goal line.
New York took the lead with four minutes remaining in the first frame when Nielsen threw a soft wrist shot on net from the right circle that was stopped by Miller, but Bailey was right on the doorstep to put home the rebound.
Just 1:17 later, New York struck again when Kyle Okposo retrieved the puck behind the net. Okposo brought the puck out front and it was poke-checked away by Miller, but the puck went right to Nielsen trailing the play and the nimble center ripped it home from the slot to give the Isles a 3-1 advantage.
"In the second period, we played really well I think," Nielsen said. "We gave up a tough one at the end there and the effort wasn't good enough in the third."
The Islanders have killed off 38 of the last 40 penalties against in their last 17 games...Nielsen's goal snapped a shutout streak of 122:30 for Miller...Islanders defenseman Travis Hamonic left the game in the third period after being struck in the face with a shot...The Islanders dropped to 16-3-5 when scoring first and 13-1-5 when leading after two periods.