Boston bounced back from its first loss of the season with Tuukka Rask shutting out the Islanders over the second half of the contest.
New York took a 2-1 lead with 10:10 to go in the second period on Keith Aucoin's goal, but Gregory Campbell tied it less than 4 minutes later.
Boston then produced the only two goals of the third -- Chara delivering the game-winner and Patrice Bergeron giving the Bruins some insurance with 6:27 remaining.
Rask finished with 24 saves while Rick DiPietro stopped 23-of-27 shots for the Islanders. New York had won its previous two games.