The only goal DiPietro allowed after just 10 shots was Todd White's 13th of the season at 18:43 of the third period.
Miroslav Satan's 12th (power play) at 14:52 of the first period started the scoring.
Ruslan Fedotenko, Marc-Andre Bergeron (power play in the second) and Sean Bergenheim also scored while Bergenheim added an assist on Satan's goal in the Islanders' first three-game winning streak since Dec. 26, 2007.
Keri Lehtonen was beaten four times after being bombarded by 49 shots for the Thrashers, who opened a five-game road trip with a 4-3 win at New Jersey Friday.
The loss cost Atlanta a share of first place in the Southeast Division.