The meeting lasted 1 hour 15 minutes and ended with a score of 6: 3, 6: 4 in favor of the former Australian Open champion.
For the 23-year-old Japanese woman, the upcoming final will be the fourth in her career at the Grand Slam tournaments.
In the previous three decisive matches, she won.
In the final of the tournament, Osaka will face either Czech Karolina Mukhova or American Jennifer Brady.
Earlier it was reported that Tsitsipas compared himself to a bird in a meeting with Nadal at the Australian Open.