Kunitz scored his 26th goal and Engelland netted his fourth. Tanner Glass scored his first goal in 26 games, a late empty-netter that sealed it for the Penguins, who won for the 15th time in 16 games at home.
Sidney Crosby, who leads the NHL with 73 points, added an assist to extend his points streak in games against Buffalo to 16 games, matching his longest streak against any team.
Fleury, who leads the NHL with 29 wins, registered his 27th career shutout.
Ryan Miller stopped 31 shots for last-place Buffalo, which has lost seven of nine.