The US did take the lead five minutes later when Carli Lloyd turned home at the far post to send her side ahead.
The chances continued to fall for the US early in the opening period, and Lloyd again struck wide with 15 minutes on the clock.
Both sides continued to attack as the half entered its latter stages, and Aya Miyama rattled the crossbar for Japan after 32 minutes.
Japan ended the half the stronger as Ohno fired just wide of Hope Solo's goal, but it remained 1-0 to the US at the break.
Both sides started the second period as they ended the first, with a host of chances falling to each team.
However, it was the US who struck a killer blow when Lloyd scored her second with a curling effort from outside the box after 54 minutes.
Japan were back in the match just past the hour mark, however, when the United States defence failed to clear and Yuki Ogimi tapped home at the back post.
Rachel Buehler came close to a third for the US after 70 minutes, but Fukumoto got down low to her left to palm the ball to safety.
Japan so nearly levelled moments later when they caused a panic in the opposition's defence, but the US just managed to shift the ball to safety.
Both sides came close in the latter stages, with Lloyd firing wide with ten minutes remaining. Meanwhile, Solo denied Mana Iwabuchi from close range moments later.
Japan could not find the leveller, however, and they had to settle for silver as the US claimed gold.