Giroux had another chance to trim the lead when he was awarded a penalty shot at 3:49 of the third, but he was stopped by Luca Boltshauser, who replaced Stephan with 7:45 remaining in the second period, after losing control of the puck.
Rookie forward Connor Bunnaman got a loose puck in the crease and scored on a backhand past Boltshauser at 15:23 of the third to make it 4-2.
With 2:10 remaining, rookie forward Carsen Twarynski battled for a puck in front and knocked it under Boltshauser to Couturier, who scored at the right post to cut it to 4-3.
"Right now, we have a few younger players that are playing extremely hard and very competitive," Vigneault said. "I need to find out a little bit more of some of our older guys, what they can do, what they can bring to the table. And we will."
The Flyers continued to push for the tying goal, but Boltshauser and Lausanne were able to hold off the late rally.
"I think as the game went on, we started playing a little bit more our game and have a little bit more confidence," Giroux said. "You want to go into the season with a high and that wasn't the case tonight."
Vigneault fiddled with his forward lines throughout the game, including four new combinations to start the third period.
"There's no doubt that I have not yet found combinations that I'm comfortable with both defensively and offensively," Vigneault said. "I've said this many times throughout camp that we have a lot of work to do. And we do. We're in the process right now, we're trying to focus on certain areas that we need to improve. And that's what we're going to try and do."
Despite a disappointing result, forward Jakub Voracek kept things in perspective with the regular season less than a week away.
"You start the season 3-0 nobody's going to remember," he said. "Lot of time it's happened where we had a good preseason and a bad start. So hopefully we turn it around and we're going to play better and have better results in the regular season."