It was Sorokin’s third shutout of the season and 25th in the NHL.
Calum Ritchie scored the go-ahead goal in the third period for the Islanders (16-10-3), who have won three in a row, including 2-1 against Tampa Bay in Elmont, New York, on Tuesday.
Jonas Johansson made 17 saves for the Lightning (16-10-2), who have lost three in a row and were shut out for the first time this season.
Sorokin kept the game scoreless at 11:42 of the second period by sliding over to deny Anthony Cirelli twice from the top of the crease during a Lightning power play. He then stopped a backhand try from Brandon Hagel just after the power play expired at 13:10.
Ritchie gave the Islanders a 1-0 lead at 12:46 of the third period with a power-play goal. Tony DeAngelo’s slap shot from the point went wide of the wide, but the puck caromed back off the end boards to Ritchie, who put his stick between his legs and banked a shot in off Johansson from the left post.
Casey Cizikas added an empty-net goal with two seconds remaining for the 2-0 final.