PSG opened the scoring in the 28th minute when Messi burst into the box and had a shot saved, before Sarabia steered the rebound home for his second goal in as many preseason matches.
Two minutes later Neymar went down in the area after a challenge from Genta Miura and coolly converted from the spot, putting further distance between PSG and the hosts.
But Gamba Osaka dragged themselves back into the game when Kurokawa scored in the 34th minute after a point-blank save from PSG goalkeeper Gianluigi Donnarumma.
The French champions soon restored their advantage, however, with Mendes darting forward to finish with his left boot and Messi combining with Neymar before the Argentina international turned in PSG's fourth goal.
Messi played an inch-perfect pass to Neymar for the Brazil forward's second effort in the 60th minute, while Mbappe's 86th-minute penalty ensured a relatively routine win for Christophe Galtier's side despite Yamami's 70th-minute effort.
PSG face Nantes next in the Trophee des Champions, played between the winners of Ligue 1 and the Coupe de France, on Sunday.