Wade Dubielewicz got the call Saturday night after Mike Dunham started two games in place of DiPietro, who is sidelined by a concussion. But Mike Comrie scored twice, and Christoph Schubert added a goal and assist as the Ottawa Senators swept the season series from New York with a 5-2 win.
The Islanders are four points out of the final Eastern Conference playoff spot, and have four games left.
"I thought Dubie played as well as he could," Islanders coach Ted Nolan said. "He was the only one who gave us a chance. Every team loses people to injuries. It doesn't mean you can feel sorry for yourself.
"We have to have some heart. We lost Ricky and (Chris) Simon and we feel sorry for ourselves. It doesn't mean you can mail it in and not try."
Dean McAmmond and Dany Heatley also scored for Ottawa, which is fighting for fourth place in the Eastern Conference. Martin Gerber stopped 21 shots to win his 15th game this season.
Viktor Kozlov and Marc-Andre Bergeron scored for the Islanders, 10th in the East. Alexei Yashin had a pair of assists for New York, winless in four games (0-3-1).
"We didn't play good defensive hockey, and haven't been in a while," Islanders forward Mike Sillinger said. "We're hanging our goalies out to dry."
Dubielewicz made his first start of the season for New York and turned aside 42 shots. Dunham lost at home to New Jersey on Tuesday and at Buffalo on Friday after DiPietro got hurt for the second time this month.
Dubielewicz made a fine right pad kick save at the left post on Joseph Corvo at 9:24 of the first period, but was matched by Gerber's left-arm stop on Viktor Kozlov's breakaway attempt with 1:34 left.
The Senators took the lead with 19.9 seconds remaining in the opening frame when Jason Spezza started a 2-on-1 break with Islanders defenseman Marc-Andre Bergeron trapped in Ottawa's zone. Spezza rushed down right wing and threw a perfectly timed pass across to Schubert, who found the open left side.
The Islanders tied it when Kozlov slammed in a pass from Yashin for his career-high 25th goal at 11:11.
Ottawa regained the lead 28 seconds later when Comrie burned newly acquired defenseman Deron Quint on a move, and beat Dubielewicz on a short shot.
"When you have a fast break and have speed, you just try to read and react," Comrie said. "If you get the defenseman's feet to turn, it's tough for him to recover."
Quint was signed by the Islanders on Friday, as injuries to regulars Radek Martinek, Bruno Gervais and Freddy Meyer left the team short on the blue line.
Comrie finished off the Islanders with his second goal of the game just 47 seconds into the final period.
"He's been playing really well like that the last few games," Ottawa coach Bryan Murray said. "He's always had the work ethic, and he goes to the net, and that's how he gets most of his goals."
The goal came as Schubert's right point shot hit off the back boards and bounced right to Comrie, who had Dubielewicz out of position.
"That goal took the wind out of the team," Dubielewicz said. "A break like that was tough."
Just as an Ottawa penalty expired, McAmmond took a back pass from Daniel Alfredsson and put a wrist shot between Dubielewicz's pads at 4:47 to make it 4-1.
After Bergeron scored on a power play with 6:02 left, Heatley wrapped up the scoring with an empty-net goal, his 48th tally of the season, with 1:40 left.
Murray's biggest concern as the Senators head to the playoffs isn't what playoff seed they hold. He'd rather the team play hard and keep on a roll.
"We're just going to try to play well every night," Murray said. "As long as the guys work hard every game, it really doesn't matter if we wind up in fourth or fifth. We've been playing well lately on the road, so it's not a concern."
Murray also had kind words for Dubielewicz's effort.
"With 47 shots on goal, you can't point the finger at their goalie and say he didn't do his part," Murray said.
Nolan, who called a team meeting for Sunday, wasn't about to concede the season.
"We still have four games left," Nolan said. "We don't give up until the last song has been sung."
Notes: D Todd Simpson, signed by the Islanders on Thursday, didn't play because the NHL honored a suspension he incurred while playing for in the German league. Simpson was suspended indefinitely for abuse of an official, pending a hearing Monday. ... The Islanders have allowed at least one goal in 15 of the 17 full periods they've played without DiPietro since he sustained a concussion at Montreal on March 13. ... The Islanders have won just twice in 17 home meetings with the Senators. They won both home games in the 2003-04 season. Ottawa has won eight straight overall against New York, dating to a 5-2 Islanders win at home on Jan. 19, 2004.