The French champions will now head to Israel to play Nantes in the French Super Cup in Tel Aviv on July 31.
Galtier, taking charge of the full squad for the first time since joining PSG from Nice this summer, said playing J-League teams in the middle of their domestic season had “forced us to raise our physical level”.
“We trained a lot, we played a lot with little recovery time,” he said, after PSG’s third game in the space of six days.
“But overall I’m satisfied both with this match and more generally with the three matches we’ve had here in Japan.”
Star forwards Neymar and Messi both played the opening 70 minutes against Gamba, and Neymar scored a first-half penalty before setting up a goal for his Argentine team-mate.
Messi then returned the favour in the second half, releasing Neymar for the Brazilian to notch his second goal of the game.
Kylian Mbappe got his name on the scoresheet with a late penalty after coming on for the final 30 minutes.
Pablo Sarabia and Nuno Mendes also scored for PSG, but Galtier was concerned by the way his team conceded two at the other end to Gamba, who lie 16th in the 18-team J-League table.
“There is still a lot of work because we conceded two goals, which is two too many,” he said.
“I hope that even when we have a substantial lead, we will be more difficult to beat when we have to defend as a team. We must be more structured.”
PSG beat J-League champions Kawasaki Frontale 2-1 in their first game in Japan last Wednesday before downing Urawa Reds 3-0 three days later.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)
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