Two well-taken goals by captain Virgil van Dijk and Crysencio Summerville either side of Keito Nakamura's conversion put the Netherlands in the lead twice but a deflected Daichi Kamada strike two minutes from time saw the spoils shared.
Six minutes after Summerville's 64th-minute goal, Koeman took off the winger in a triple substitution and later added a third centre back in Nathan Ake.
The more defensive setup backfired, though, with Japan seizing the initiative and Ogawa firing a header goalward to set up Kamada's equalising deflection. Koeman, however, said he had no regrets about his tactics and that shoddy defending was to blame.
"There was also a problem with pressure on the flanks. So if you look at the game, both goals, well, we didn't defend well," he told reporters.
"Football is a funny game because, after Japan scored the second goal, they started defending as well. "So we could have scored a third goal. So I don't regret my choices."
A day after declaring Memphis Depay as fit to start after recent thigh trouble, Koeman had the Netherlands' all-time top goal-scorer come off the bench in the second half, replacing the lively Donyell Malen. Depay earned a yellow card for a rough challenge and was unable to make a difference.
The Netherlands, quarter-finalists at Qatar 2022, have nearly a week's break before they face Sweden in their second Group F match in Houston.
Koeman said the Netherlands played at a "minimal standard" against the Japanese and accused the media of under-rating their Asian opponents.
"Of course we can perform better and we need to grow during the tournament," he said.
"This definitely was not our best performance. "Of course, we would have preferred to win the first game. We expected to."