Robitaille picked off a clearing attempt on the left side and launched a 45-foot slap shot that got past a screened Ryan Miller to give the Islanders their first win at home since Dec. 26. They were 0-3-1 since.
Andy Hilbert added an insurance goal with 53.9 seconds left.
Arron Asham scored twice and Trent Hunter also scored for the Islanders, while Rick DiPietro, yanked after allowing three goals on five shots Friday night in Atlanta, made 25 saves for the win.
It was just the third time this season New York won when trailing after two periods (3-9-0).
Jochen Hecht scored twice for the Sabres, while Ales Kotalik added a goal. Buffalo lost its third straight game for the first time all season. Miller stopped 26 shots.