The Rangers remained tied for seventh place with Buffalo in the Eastern Conference playoff chase and missed a chance to move into a share of sixth place with Montreal.
Comeau scored his 22nd goal of the season 3:24 into the middle period to forge a 1-1 tie and Radek Martinek put the Islanders ahead on a slap shot 33 seconds later.
Jesse Joensuu and P.A. Parenteau added goals later in the period and the Islanders increased their advantage to 6-1 with third-period tallies from Matt Moulson and Trevor Gillies.
Al Montoya made 25 saves for the Islanders, who had lost their previous three games.
Henrik Lundqvist surrendered four goals on 22 shots through two periods before giving way to Chad Johnson.