Karl scored his first goal for the club and collecting the Man of the Match award on his full European debut.
Karl opened the scoring in the fifth minute with a stunning left-foot shot into the top corner after a slick Bayern move, before Harry Kane, Luis Diaz and Nicolas Jackson completed the rout at the Allianz Arena.
The result strengthened Bayern's position in the league phase standings, moving them to second place with nine points from three wins, and underlined the depth of attacking talent available to manager Vincent Kompany.
Speaking after the match, Karl said he was thrilled to make such an impact at this stage of his young career. "I had goosebumps when hearing the Champions League anthem," he said. "It's a dream come true for me. Winning the Man of the Match award is amazing, but I won't stop, I'll keep working hard and keep learning."
The teenage winger, who joined Bayern in 2025, also spoke about the significance of his breakthrough moment. "Scoring my first Champions League goal on debut is something I'll never forget," he added. "Now that I've scored my first goal, a lot of people will be watching, but I'll keep going with confidence."
Karl's composure and awareness throughout the match impressed both teammates and supporters, with Kompany later praising the youngster's maturity.
"Lennart showed great confidence and understanding of the game, he's always been very dangerous and can score," the Bayern coach said. "He deserved everything tonight, and we need to stay calm around him as he develops."
The victory extended Bayern's perfect start to their European campaign, while Karl's breakthrough performance, making him the youngest Bayern scorer in Champions League history at 17 years and 242 days, gave fans another glimpse of the club's next generation of talent.
Liverpool's dominant 5-1 Champions League victory over Eintracht Frankfurt was overshadowed by a major injury setback, as Jeremie Frimpong suffered a recurrence of his hamstring problem that will keep him out for several weeks.
Bayern Munich have made it clear that Michael Olise is not for sale, with sporting director Max Eberl confirming there is no release clause in the French winger's contract despite growing interest from top European clubs.
Manchester City are facing several late fitness tests as they prepare to visit Aston Villa on Sunday, with key midfielder Rodri among those in doubt.
Arne Slot said Liverpool's dominant 5-1 Champions League victory at Eintracht Frankfurt had been the perfect response to their recent struggles, describing it as "a big, big difference" from their previous performances.
