Though you're right, I think it would be fair to say the momentum changed when he was brought on. Japan were camped in their own half, and Mitoma immediately started driving with the ball at the German defence, pushing them back and moving Japan up the field. Wonderful result! SUGOI!He did, yes.
I think it's a bit much to say *HE* changed the game, but it's certainly true that the group of substitutions made by Japan, which included our boy, turned the game round.