Mainz goalkeeper Robin Zentner had to be on guard to defuse Dani Olmo's effort in the 4th minute before Marcel Halstenberg headed just wide from a promising position four minutes later.
Behind Bayern's attitude stands the intention to map the team's hierarchy in the player's salary.
Plans about the club's structure will be made in close contact with its 160,000 members who have to vote on any significant changes within the club.
Raul Jimenez put the away side in front with a half-volley from Castelo Podence's left-wing cross, before Romain Saiss's header from Neto's corner completed the scoring.
Zinedine Zidane's side didn't play in the first round of matches one week ago, after their game at home to Getafe was postponed in order to allow them more time to recover after their participation in last season's Champions League in August.
After selling Ivan Rakitic to Sevilla, Barca are currently looking to sell striker Luis Suarez, with Juventus a possible destination, while Arturo Vidal is close to joining Inter Milan.
Also absent were midfielder Arthur Melo, who joined Juventus from Barcelona in July, Flamengo striker Gabriel Barbosa and Real Madrid left-back Marcelo. Sao Paulo's defender-turned-midfielder Dani Alves is unavailable because of a fractured forearm.
The 23-year-old's displays last season earned him his first cap for Spain on September 6th as he started in his country's 4-0 UEFA Nations League win against the Ukraine.
XI'AN, Sept. 15 (Xinhua) -- Northwest China's Shaanxi province marked the one year countdown to the 14th National Games with a ceremony gala on Tuesday.
Flamengo remain second in the group with six points from three matches but with a negative goal difference.
Chengdu Xingcheng Habitat is the other team which notched up two wins from the first two rounds of the second-tier league. They beat Beijing BSU 2-0 in a second-round fixture on Wednesday.