The Japan midfielder was also in the Hoops side for their game against Gretna on Monday afternoon.
And though he was forced off during the 5-0 victory with an ankle injury, Mizuno is delighted to have started playing for his new club.
"Since I signed, four reserve games have been called off," he told Celtic View. "So for myself, and the club, the Rangers game was a really important match and I was just glad to get to be involved in that kind of fixture. "We managed to get a good result, which was important as well.
"I felt comfortable playing in the game and I was happy, as well as relieved that I'd managed to play my first game in Scotland.
"It is a bit more physical. You find the players are that bit taller and sometimes you get challenges when you don't expect it.
"In the Rangers game, there were some tackles from behind and that doesn't really happen in Japan. But overall, I don't see a big difference in style."
Mizuno is hoping to break through in the first team squad alongside fellow countryman Shunsuke Nakamura before the end of the season. He said: "My main target is to win a place on the bench for the first team over the next few months.
"But in order to do that, I know that I need to earn the right by doing well for the reserves.
"Of course, I want to play for the first team but to start with I might need to come on as a substitute and take it from there."