When 20 minutes of hockey that was total domination for the Flyers and absolute humiliation for the Pittsburgh Penguins was over, Peter Laviolette returned to the home dressing room at Wells Fargo Center to warn his team about a letdown.

Flyers players talked about it among themselves, too.

Then they went back out for the second period and blew everything they’d worked for, and eventually what seemed would be an easy and satisfying victory turned into a terrible 5-4 loss.

“We play like that, it’ll be a long summer,” Flyers winger Scott Hartnell said after his team blew a 4-1 lead and lost in regulation for the first time since doing so in a 7-3 loss in Detroit on Jan. 17, 1993.

This loss left the Flyers starting their second half of the season just as they did the first, with a home loss to their hated rival.

Afterward, Claude Giroux called it the worst loss in what’s been a disappointing season.

“Yeah, when you’re up 4-1, you gotta find a way to close the game up,” the Flyers captain said.

The Flyers built their big lead in a first period in which they outshot Pittsburgh 18-4, and in the process Penguins goalie Marc-Andre Fleury sure looked rattled letting in a terrible goal before getting yanked.

“We talked after the first period that the Pittsburgh Penguins are not going to sit back and just hand over two points,” Hartnell said. “They were going to come back, and lo and behold, before we know it, it’s 4-4.

“We just can’t do that. It’s embarrassing to the fans. It’s embarrassing to one another and we let another two points slip away.”