The Catalan giants, five-time winners, made amends for their defeat by Monaco in their first match by thumping their Swiss visitors.

Raphinha and Inigo Martinez strikes as well as an own goal helped Hansi Flick's side secure a sizeable victory and boost their goal difference significantly.

"We knew after the game against Monaco in the Champions League we had to give a quick reply in the next game, which was this one, and we did that well," Raphinha told Movistar.

"A couple of days ago we lost a game in La Liga too (at Osasuna) and we had to give a quick response, and we did that.

"It's much easier playing here at home because of the joy (the fans) give us."

Raphinha said with the expanded Champions League format and one table for all the teams, it was useful to build a good goal difference.

"It's important to score so many goals because at the end of the eight games, it will be handy," he added.

Barca coach Flick rolled out arguably his strongest available team after the loss at Monaco, despite the Swiss side's struggles.

Young Boys are in the relegation zone of their domestic league with just one win in eight games and were thrashed at home by Aston Villa on their European debut this season.

It took Barcelona just eight minutes to move ahead, with Lewandowski applying a poacher's finish to Raphinha's cross-shot.

Jules Kounde hammered over and Ferran Torres had a shot saved as Barcelona dominated, but Young Boys carved out a first opening after 30 minutes when Ebrima Colley pulled an effort wide.

Raphinha, enjoying a strong start to the campaign, doubled Barcelona's lead from close range after Pedri's shot was blocked but the ball ricocheted to his feet.

Centre-back Martinez headed home Barca's third from Pedri's free-kick shortly afterwards as the Catalans overran their ragged visitors.

- Barca romp -

Torres wasted a fine chance for the fourth when he fired straight at Young Boys goalkeeper Marvin Keller when well placed to score.

Lewandowski netted his second with a close-range header after Martinez had nodded Lamine Yamal's corner back across the face of goal as Barcelona began the second half just how they finished the first.

It was the 36-year-old's ninth goal in 10 games this season as he enjoys a revival under his former Bayern Munich coach Flick.

Young Boys winger Joel Monteiro struck the crossbar but that was as close as the visitors came to joy in Catalonia.

Barcelona fans were pleased to see Dutch midfielder Frenkie de Jong come on as a substitute for his first appearance since an ankle injury in April as the game petered towards a close.

"For Frenkie today was an important step, to come back to the team after having suffered such a serious injury, playing some minutes today was important for him," said Flick.

"We need to support him to get him back where he was. For that we need time and I'll give him time. I'm willing to make it my personal mission, he deserves it.

"I see a lot of things I like from him, that's why he deserves our trust, and patience as well."

Mohamed Camara deflected Alejandro Balde's cross into his own goal for Barcelona's fifth in the 81st minute.

Home supporters chanted the name of former Barca midfield icon Andres Iniesta, after reports the Spanish 2010 World Cup winner will announce his retirement next week.

Monteiro had a late goal ruled out for offside and Inaki Pena made a smart save at his near post late on, with Polish goalkeeper Wojciech Szczesny watching on from the presidential box.

Barcelona are poised to sign the former Juventus and Arsenal stopper to replace the injured Marc-Andre ter Stegen.