The United States beat Japan 2-1 on Monday in an inconsequential game to end round-robin play.
But the U.S. team's failure to record a hit against a third-string Japanese pitcher until the sixth inning demonstrated the challenge it faces in the gold-medal matchup between the two teams.
U.S. batters did race their way into three hits and a run against Yamamoto Fujita in the sixth, and Kelsey Stewart shot a tie-breaking homer to end the game an inning later.
But, as United States' 3-1 loss to Japan in the Beijing 2008 finals showed, counting on lucky hits late in the game delivers inconsistent returns. Failing to hit in key moments foiled the United States against Yukiko Ueno of Japan in 2008, the last time softball appeared at the Olympics.
Ueno, 39, will be back in Tuesday's final, as will U.S. hurlers Cat Osterman and Monica Abbott.
Overall, the United States finished round-robin play on Monday scoring nine runs on 27 hits with Stewart's blast over right their lone home run. By contrast, Japan had double the runs on 26 hits, including six homers, and stranded fewer runners.
On Monday, both teams used their back-up pitchers and several bench players. The win means the United States will bat after Japan in the final.
The rivals went unbeaten against their other four competitors at Tokyo 2020 to set up the 2008 rematch, when Japan became the only team other than the United States to capture gold. The two rivals also have met for the last seven biennial World Baseball Softball Confederation world championships, with U.S. taking five of them.
Tokyo 2020 organizers returned softball to the Olympics, and both the hosts and their opponent have said in the long lead-up to the postponed competition that they hope an exciting final can boost interest in the sport and make it a recurring fixture.
Later Monday, Mexico beat Australia, 4-1, to face Canada in Tuesday's bronze medal game.
Clouds hung over the ballpark on Monday, and Tuesday's forecast calls for rain.
Canada has played in each Olympics, but never placed higher than fourth. Mexico made their Olympics debut this year.