UNIONDALE, N.Y. (AP) -- The Pittsburgh Penguins picked a perfectly poor time to take a night off.
Fresh off a big home win over New Jersey on Saturday and facing another key matchup with the Devils on Tuesday in the tight Atlantic Division race, the Penguins never showed up against the New York Islanders and paid for it.
Bill Guerin had a goal and assist in the decisive second period for the also-ran Islanders, who prevented the Penguins from clinching a playoff spot Monday night with a 4-1 victory.
"I hope every team takes us a little bit for granted," said winning goalie Wade Dubielewicz, who made 28 saves. "We have a feisty group in here."
Pittsburgh holds a two-point lead over New Jersey in the divisional race, but missed a chance to double its advantage heading into a road meeting with the Devils on Tuesday. The Penguins dropped three points behind Montreal in the fight for first in the Eastern Conference with six games left.
"Really, really disappointed with the performance," Penguins coach Michel Therrien said. "I'm speechless about their effort, I'm speechless about their concentration and their will to win this game."
Penguins captain Sidney Crosby sat out his sixth straight game and 27th in 30 because of a sprained right ankle, but is close to returning -- perhaps on Tuesday. Pittsburgh is 15-8-4 without him, but had gone 4-1 with 27 goals in the first five games of his latest absence.
"Honestly, I just thought we played harder," Guerin said. "We had everybody finishing their checks, moving their feet better. I think that was the difference."
One day after their 4-1 loss at Philadelphia eliminated them from postseason contention, the Islanders put a crimp in the Penguins' playoff plans in a classic trap game.
Sandwiched between a pair against New Jersey, the Penguins didn't respond to the challenge of taking care of a team that had nothing to play for. Pittsburgh came off a 7-1 home victory over the Devils on Saturday, but fell to 4-3 this season against the Islanders.
"We obviously weren't on our best game," forward Jordan Staal said. "We just came out flat. We were a little sloppy. There is no excuse for it. We should've been ready for this game, and we weren't.
"It's a lot nicer that we don't have to think about this game too long before our next big game comes up. We're going to learn from this mistake and hopefully we'll be ready for a big game [Tuesday]."
Petr Sykora had the lone goal for the Penguins, who started Ty Conklin in goal over Marc-Andre Fleury. Conklin got his second start in five games because of the back-to-back contests and for his career-best, 50-save effort in a 4-2 win over the Islanders on Feb. 26.
He finished with 32 saves.
New York, which had lost seven of eight, took control in the second period, scoring twice and outshooting the Penguins 14-3 after the teams recorded 12 shots each in the first.
"I don't know if they were 100 percent into this game or if we just played so well," Bergenheim said.
Guerin drilled a shot off the post behind Conklin about 8 minutes into the period when the game was tied 1-1. He refined his aim with 8:15 left, wristing in a shot -- another that clanged off the post.
The lead grew to 3-1 just 3:08 later when Conklin left a rebound off another shot by Guerin that was put in by Bergenheim at the left post.
"We were kind of OK in the first period, but after that we didn't play our game," Therrien said. "The work ethic was not there. They worked harder than us. It's pretty simple. That's why they won.
"It was an emotional game last game. Maybe that was one of the reasons why we were flat. It's unacceptable. Excuses are for losers."
Park gave the Islanders a short-lived 1-0 lead 3:22 into the game, scoring his first goal in 28 games and New York's ninth short-handed tally. Kyle Okposo got the puck away from defenseman Sergei Gonchar at the right point, and found Park with a pass. Park wound up above the right circle and ripped a shot past Conklin.
Okposo, the Islanders' top prospect, has a goal and two assists in his first four NHL games.
Sykora tied it 36 seconds later, before Jeremy Colliton's high-sticking penalty expired. Sykora beat Dubielewicz with a drive from the bottom part of the right circle for his seventh goal in seven games and 28th overall.
Penguins RW Pascal Dupuis missed the game to be with his wife who gave birth to daughter Zoe on Monday morning in Atlanta. ... D Robert Scuderi, who broke his finger against the Islanders on Feb. 26, returned to the Pittsburgh lineup after an 11-game absence. ... C Mike Comrie, one of three Islanders to play in New York's first 76 games, sat out with the flu.