Marcus Rashford netted his fifth goal of the season thanks to a well-worked move involving Dani Olmo.
Napoli had little time to recover before FC Barcelona doubled their lead.
Napoli struggled to make an impact in the first 45 minutes, failing to register a shot.
Barcelona and Real Madrid are touring the United States this summer as part of their preparations for the start of the new season.
Bayern bosses have said they would not let him go but are reportedly ready to listen to offers of €50 million ($50 million) or more.
The awards will be presented at the 2020/2021 UEFA Champions League group stage draw ceremony on October 1.
