"Mike Dunham is a great goaltender," said Islanders forward Jason Blake after the Senators chased New York's replacement starter from the game with five goals on 28 shots en route to a 5-2 victory. "It doesn't matter who's in net - Mike, Ricky or Martin Brodeur - if you hang him out to dry, there's not much he can do back there. It wasn't his fault."
Joe Corvo and Dean McAmmond each had a goal and an assist and the Senators, playing before a sold-out crowd of 19,989 at Scotiabank Place, compounded the misery for the Islanders, who were forced to start without their injured No. 1 goaltender for the first time since Feb. 1.
DiPietro is listed as day-to-day with a sore neck after being injured in a collision with Montreal's Steve Begin in a loss to the Canadiens on Tuesday.
The Senators took a 2-0 lead then buried the Islanders with a third-period explosion in which they scored three times in 76 seconds.
"It was unacceptable," Islanders forward Ryan Smyth said of New York's second straight defeat and fourth in the past five games. "We're in a playoff race and we've got to find a way to step up our game or we're going to be on the outside looking in."
Ottawa (41-23-7) received goals from unlikely sources.
Corvo's was his first in 26 games and Chris Neil scored his first in 20 games.
Chris Kelly and Jason Spezza also scored for the Senators, who won for the second straight game and seventh time in a row against the Islanders.
Antoine Vermette and Mike Comrie each added a pair of assists for the Senators and Dany Heatley set up Spezza's goal to extend his point streak to 16 games.
Ray Emery made 28 saves to pick up the victory in goal.
In the past 41 meetings between the teams dating back to Feb. 12, 1996, Ottawa's record is 29-4-8-0, including 3-0 this season.
The victory also allowed the Senators to leapfrog the idle Pittsburgh Penguins for fourth place in the Eastern Conference standings with 89 points.
"It's a game that we've got to build on," said Corvo, who hadn't scored since Jan. 7. "Everybody going on all cylinders."
Miroslav Satan had a goal and an assist for the Islanders (34-26-10) and Drew Fata, with his first NHL marker, also scored.
The Islanders began the night clinging to seventh place in the Eastern Conference standings, even on 78 points with the Carolina Hurricanes, who lost 3-2 to the New Jersey Devils on Thursday.
Dunham gave way to Wade Dubielewicz in the third period with New York trailing 5-0.
He made his first start in 19 games and there wasn't much he could do about Kelly's opening goal early in the second period.
He didn't look sharp on Corvo's goal less than four minutes later that made it 2-0. Corvo threw the puck at the net from the side boards and it took a deflection off the skate of Islanders defenceman Marc-Andre Bergeron and fooled the goaltender.
Ottawa then blew the game open early in the third when Neil scored on a wraparound two minutes in to set off a flurry that would spell the end of the night for Dunham. The three-goal outburst by Ottawa that came in one minute, 16 seconds, marks a franchise record for the club.
"We've got to step up and everybody's got to play a part in our zone, all five guys, and we weren't doing it tonight," Smyth said.
Neil hadn't scored since Jan. 27 and it was only his second goal in the past 39 contests.
"It's one of those things as long as we win," Neil said. "I'm not really here to score goals, I'm here to create openings for other guys. If I can chip in, that's great."
McAmmond cashed in a rebound 24 seconds after that and 52 seconds later, Spezza capped off a tic-tac-toe passing play with Heatley and Patrick Eaves for his 29th goal of the season.
Spezza now has at least a point in his past 15 games (nine goals, 17 assists), although it's not recognized as an official streak because he sat out a game with an injury.
Dubielewicz, making his first appearance of the season after being recalled from AHL Bridgeport on Wednesday, replaced Dunham following the goal and made eight saves the rest of the way.
Satan broke Emery's shutout bid late during a 5-on-3 power play and Fata got credit for a goal from a scramble with 4.2 seconds left.
Notes: Neil's goal was his 100th NHL point. . . . Forward Oleg Saprykin was a healthy scratch for the Senators for the second straight game. . . . Ottawa plays host to Philadelphia on Saturday. . . . Bergeron appeared in his 200th career game. . . . Islanders defenceman Sean Hill was a scratch. . . . The Islanders travel to Florida to face the Panthers on Saturday and wrap up their road trip Tuesday at Tampa.