The game is also a rematch of the 2007 Women's World Cup semifinal, which the Brazilians won, 4-0.
Angela Hucles scored two goals as the Americans rallied from a 1-0 deficit to sweep past the spirited but overmatched Japanese. A goal by left back Lori Chalupny just before halftime gave the USA a 2-1 lead and Heather O'Reilly, who set up Hucles' first goal, scored the eventual gamewinner in the 71st minute.
Two of the Americans' goals came on what seemed to be crosses when O'Reilly and Hucles' struck balls from wide positions on the right flank, yet they proved to be superior despite starting sluggishly and falling behind to Shinobu Ohno's goal in the 17th minute.
Lindsay Tarpley failed to vacate the six-yard box after the Americans only partially cleared a Japanese corner kick and Yukari Kinga centered the ball to Ohno, who had ample time to settle it before sticking it past keeper Hope Solo as the Americans appealed for offside.
Solo kept the score at 1-0 a few minutes later by turning away a low shot from Yuki Nagasato, who had troubled the USA when the teams met in the group phase but whose influence in this match waned after a bright start.
The Americans gradually clamped down after Solo's save and with midfield playmaker Homare Sawa stifled in the middle and Nagasato neutralized out wide, they began to overpower Japan on the flanks. Rather than bombing balls up the middle as they had often done in the group phase, the defenders used their possessions to link through midfield.
With Rodriguez stretching the Japanese by intelligent, sharp runs and Hucles working the space underneath her, central midfielders Carli Lloyd and Shannon Boxx kept the middle secure and gobbled up clearances to send the ball right back into Japan's defensive third.
O'Reilly, a force during most of this tournament with her energy and drive, set up the first goal in the 41st minute by powering her way to the end line and cutting back a ball that Amy Rodriguez missed, Lindsay Tarpley dummied, and a wide-open Hucles tapped into the net.
The subtle yet vital skills of Rodriguez and Chalupny's zeal to attack came into play as the stunned Japanese anxiously awaited the halftime whistle. Rodriguez checked back and out wide to control a pass from Lloyd, who'd received it from defender Kate Markgraf.
Rodriguez relayed the ball to Chalupny, who instead of going to the goal line cut inside and cracked a rising right-footed shot over the outstretched hand of keeper Miho Fukumoto and under the crossbar.
Fukumoto is a decent enough shotstopper, but at 5-foot-5 and lacking a great leap, is vulnerable to high balls, a weakness the Americans would exploit, intentionally or not, in the second half as they overran Japan in all areas of the field.
O'Reilly's cross/shot from midfield and near the right touchline soared over Fukumoto and off her fingertips in the 71st minute; Hucles sent over a ball from near the touchline 10 minutes later that the keeper could only deflect just under the crossbar.
A header off a free kick flashed wide of Solo's goal in the final minutes, and in stoppage time Nagasato shook free of her shacklers long enough to hit the post from close range, and then square the rebound for Eriko Arakawa to tap in during a scramble.
The goal, though meaningless in terms of the outcome, rewarded Japan for a memorable achievement: its first semifinal appearance in a worldwide soccer competition. It plays Germany Thursday in the third-place match.
Hucles' double gives her the team, and tournament, lead with four goals. O'Reilly has netted twice, and Natasha Kai, Lloyd, Chalupny, Rodriguez and Tarpley have scored one apiece. O'Reilly leads the team with three assists; seven other players have each registered one.
It has taken the Americans some time to wean themselves off dependency on Wambach and diversify their attack, as reflected by the scoring statistics and epitomized by the buildup and surprising strike on Chalupny's goal.
In the 2004 Olympic final, Wambach scored the winner against Brazil 22 minutes into overtime; for the 2008 renewal, several players can step up should the situation demand it.
GAME SUMMARY (Semifinal)
Aug. 18 in Beijing
USA 4 Japan 2. Goals: Hucles 41, Chalupny 44, O'Reilly 70, Hucles 80; Ohno 16, Arakawa 94+.
USA -- Solo, Mitts (14- Cox, 86), 15-Kate Markgraf, 3-Christie Rampone - Capt., 17-Lori Chalupny; 9-Heather O'Reilly, 7-Shannon Boxx, 11-Carli Lloyd, 5-Lindsay Tarpley (6-Natasha Kai, 67); 8-Amy Rodriguez (12-Lauren Cheney, 83), 16-Angela Hucles.
Japan -- Fukumoto, Kinga, Ikeda, Iwashimizu, Ando (Hara, 56), Yano (Maruyama, 73), Miyama, Sawa, Sakaguchi, Ohno Arakawa, 71), Nagasato
Yellow cards: USA -O'Reilly 39, Mitts 50.
Referee: Nicole Petignat (SUI)