Colin Greening had the other goal for Ottawa (9-6-2).
Benoit's goal at 8:37 of the second period made it 2-0 for Ottawa and came a little more than two weeks after he thought he originally had his first back on Feb. 3 in Montreal. But a questionable goaltender interference penalty that day on Jakob Silfverberg negated the goal.
Fittingly, Silfverberg made a nice pass to Benoit on Tuesday's one-time goal past DiPietro.
Hamonic's wrist shot at 2:44 of the third period cut the Ottawa lead to 2-1 and ended a scoreless streak of 103:19 for the Islanders.
Dziurzynski gave the Senators a 3-1 advantage at 17:25 of the third with his first NHL goal in just his third game. DiPietro couldn't handle the big left-winger's initial shot and Dziurzynski poked the rebound home. Senators rookie defenceman Eric Gryba picked up an assist for his first NHL point.
Following a scoreless opening period that featured just fifteen shots, Greening opened the scoring for a struggling Ottawa power play that came in on an 0-for-24 slump.
With five Islanders, including DiPietro, around him, Greening jammed in a loose puck home for his second of the season at 6:01.
Beniot then added his first in the NHL off a feed from Silfverberg just 2:36 later.
The Islanders poured on the pressure, but as he has so many times this season for the injury-riddled Senators, Anderson held the fort until Harmonic found a way through early in the third.
Notes: The Senators were 1-for-3 on the power play, while the Islanders went 0-for-4. ... Chris Neil reached 1900 penalty minutes for his career, all with the Senators, in Monday's win at New Jersey ... Islanders defenceman Matt Carkner missed his homecoming Tuesday as he sat out the game with a groin injury. Carkner, a native of Winchester, just outside Ottawa, spent three seasons with the Senators before signing with the Islanders in the off-season. ... Matt Moulson has played in 262 consecutive games, which is the fourth longest streak in Islanders' history.