The Islanders, seeking their first trip to the post-season in seven years, improved to 5-0-1 in their last six games. They started the day tied with Ottawa and the New York Rangers with 44 points.
New York kept pace with Ottawa, which won at Philadelphia. The eighth-place Rangers were idle.
The Bruins fell to 5-2 in their last seven games one night after moving into second place in the East with a 5-4 win at New Jersey.
Bailey's fourth goal in six games and ninth of the season snapped a 1-1 tie at 13:12 of the second period. Tyler Seguin had tied it for Boston earlier in the period.