The two-goal flash woke up the Islanders, who responded with one of their own. Andrew Ladd scored his first of the preseason in impressive fashion, beating Schneider cleanly upstairs from the high slot at 14:29.
This time, the Islanders did carry their momentum into the third period. Stephen Gionta - the game's first star - scored against his former team, crashing the net and knocking the go-ahead goal in at 3:55. Barzal scored the eventual winner shortly after, putting the Islanders up 4-2 at 6:30.
Devante Smith-Pelly chipped a rebound past Thomas Greiss at 11:43 to make it 4-3, but that's as close as the Devils came. Travis Hamonic foiled the Devils best chance at tying the score in the final minutes, sweeping a loose puck out of harm's way and under Greiss.
Greiss made 25 saves for the win in his preseason debut, his first action since returning from the World Cup of Hockey.
"It's always nice to play, you just want to get in there, play a couple games, get a feel for the game and get your timing down," Greiss said.
Boychuk also made his preseason debut, picking up a pair of assists. The Isles defenseman had previously been sidelined with an upper-body injury.
"I felt pretty good," Boychuk said. "I think it went well for the first game. Just getting back out there feels good. You want to play as many games as you can to get ready for the season."
The Islanders are currently in a stretch of three games in three nights. They'll host the New York Rangers on Tuesday night at Barclays Center at 7 p.m., before heading to Prudential Center for a rematch with the Devils on Wednesday night.