Reds boss Jurgen Klopp played a full strength side with captain Jordan Henderson, summer signing Joel Matip, Lallana and Emre Can all starting.
Can started his second consecutive game for the Reds but only played the opening 45 minutes as he did yesterday.
The Liverpool star returned to training last week joining the squad towards the end of the US tour after an extended break following his Euro 2016 duties.
Can was part of the Germany squad that reached the Euro 2016 semi-finals, losing to hosts France in the penultimate game.
The 22-year-old midfielder was one of three ethnic Turks born in Germany that featured in the clash with the other two being Mainz youngster Suat Serdar and star forward Yunus Malli.
Malli actually scored one of the goals for the Bundesliga outfit after coming on as a second half substitute for Jhon Cordoba on 51 minutes.
Mainz 05 4-0 Liverpool
Kick-Off: 14:45 GMT
Liverpool: Manninger, Arnold, Wisdom, Matip, Moreno, Grujic, Can, Henderson, Lallana, Origi, Woodburn
Mainz: Lossl, De Blasis, Balogun, Bell, Donati, Rodriguez, Serdar, Clemens, Brosinski, Onisiwo, Cordoba
Goals: Brosinkski, Cordoba, Malli, Muto