Despite their nickname Nadeshiko - a flower symbolising grace and beauty - the Japanese have earned a reputation as giant-killers by knocking out the hosts in the quarter-finals and Sweden in the last four.
They face a formidable challenge in the USA - traditionally the super-power of women's football - who are bidding for a third World Cup title after their victories in 1991 and 1999.
History is against the Japanese who have never beaten the Stars and Stripes in 25 meetings with the USA enjoying 22 wins to three draws: in those games, the USA have scored 77 goals while the Japanese have netted only 13 times.
But Sasaki says his side have got stronger as the tournament has progressed and feels this is their time.
"We won against Germany and Sweden, that was empowering and it helped to let us know how strong we really are, the players have got stronger so why not tomorrow?," he said.
"As trainer of Japan, I have lost five times to America, so this is a good time for the gods of football to give me a victory over them."
Japan have already played the USA three times in 2011 - twice in warm-up games in May, when the USA won 2-0 on both occasions, and the Stars and Stripes beat the Japanese 2-1 at the Algarve Cup in March. But Sasaki says much has changed since then.
"When we played the US team in May, they were already in good shape, but the Japanese team had only just assembled and weren't in as a good condition, so losing wasn't that surprising," he said.
"We didn't have much time to prepare for this tournament and we have developed game by game and got better and better. We want to try and take this experience through to the London Olympics."
Japan captain Homare Sawa is a contender for player of the tournament and says her side are determined to make history by beating the USA.
"We came here to go for the top and now the football gods have offered us the chance and the stage to do that, even against America," said Sawa.
"We don't feel the pressure, we just want to take our chance. We have to give 100 per cent and work together, we have to work hard to steal balls in defence."
Having played in five World Cup tournaments, the 32-year-old refused to say whether victory on Sunday could lead to her retirement.
"I am not thinking about the future right now, just about tomorrow's match, nothing past that," she said.