PITTSBURGH -- It was Halloween Night at PPG Paints Arena on Tuesday and fans were encouraged to come to the game in costumes.

The Flyers came disguised as an AHL team in the opening period.

In their worst period of the young season, the Flyers’ defense was non-existent as it gave goalie Brian Elliott no support. Their attack time was barely noticeable, and they fell into a 4-0 hole en route to a 7-1 loss to the arch-rival Pittsburgh Penguins.

“He’s been really good for us. Battling his butt off,” defenseman Matt Niskanen said of Elliott, the NHL’s No. 3 star of the week. “Not much of a chance tonight. Backdoor looks. Extra whacks. That’s stuff that just can’t happen. We’re going to work to get better at it and to fix it, but we left him hung out to dry."

Pittsburgh skated circles around the Flyers (5-5-1) in the opening 20 minutes and used a swarming forecheck to keep the visitors pinned in their own zone. As a result, the Penguins had a 16-6 shots domination in the period and got goals from Justin Schultz, Jared McCann, Dominik Simon, and Sidney Crosby.

“It was horrible. Embarrassing. We didn’t come out strong. They were ready and they gave it to us," center Sean Couturier said. “It’s tough winning games when you allow three, four goals in the first period. We’re going to have to learn from it. That’s twice in a row where we gave up [at least] three goals in the first period. We’ll have to be better."

The Flyers had dominated games in this arena since it was opened in 2010, compiling a 14-3-3 regular-season record here entering Tuesday.

But the Penguins, who have overcome a slew of injuries to start the season with an 8-5 record, scored three first-period goals in a 2-minute, 49-second span to take control.

Schultz scored when his flip from the point got past a screened Elliott to make it 1-0, and an all-alone Jared McCann tapped in a pass in front to put the Pens ahead, 2-0. An uncovered (notice a pattern?) Simon made it 3-0 from the right circle, and Flyers defenseman Travis Sanheim (minus-4) fell down to give Pittsburgh a three-on-two that Crosby finished with a right-circle shot past a screened Elliott.

Captain Claude Giroux, who led the Flyers with six shots and won 61 percent of his faceoffs, pointed a finger at himself and the veterans on the team.

“It’s embarrassing the way we played,” he said, before bringing up Sunday’s not-as-close-as-it-looks 5-3 loss to the Islanders. “We didn’t have a good game in New York and we came here and needed to rebound with a good game. It starts with the older guys. I’ve got to be better; the veterans need to be better. We need to be ready for these games.”

Crosby, who wore a protective cage because he got hit in the face in his previous game, finished with a goal and two assists; he has 42 career goals (the most he has scored against an opponent) and 102 points against his Pennsylvania pals.

Late in the second period, with Elliott surprisingly still in the nets, Jake Guentzel and Zach Aston-Reese scored 20 seconds apart, increasing the Penguins’ lead to 6-0. Carter Hart replaced Elliott at the start of the third period.

Oskar Lindblom’s sixth goal ended Matt Murray’s shutout bid early in the third.

So much for building momentum from a late five-goal outburst that erased a 4-2 deficit Saturday and gave them a 7-4 win over Columbus.

Giroux said he didn’t know if it was a lack of energy or a lack of playing smart that led to Tuesday’s first-period collapse.

“Whatever it is, I don’t really give a [bleep],” he said. “We need to figure it out and play the right way. When you’re a professional athlete, you have to be able to show up every night.”

The Flyers will try to regroup Friday in New Jersey, a team they defeated, 4-0, in their home opener. Since then, they have just three wins in their last nine games.