BEIJING, Aug. 15 (Xinhua) -- The United States dominated the softball field here on Friday as the three-time defending champions pounded two world's powerhouses at the Beijing Olympic Games.

    In their first game of the day, the Americans only used five innings to shut out the previously undefeated Japan 7-0.

    Leadoff batter Natasha Watley and Jessica Mendoza each delivered a home run in the first inning to stun the runner-up at 2006 World Championships.

    Slugger Crystl Bustos jumped into the home run derby in the fourth inning, sending the ball directly to the center field stands after Mendoza launched her second homer in this inning.

    Bustos's home run not only bettered her own Olympic record by one as she has 11 now, also gave the U.S. team possession of the Olympic record for most home runs (four) by a team in a single game.

    Japan's starting pitcher Naho Emoto and Mika Someya just could not stop allowing base hits, giving up three more runs to suffer their first defeat of the tournament.

    "Our offense is so strong. There is a quote, 'your best defence is a good offence'. We had to play hard," said the USA's pitcher Monica Abbott.

    After about 30-minute rest in the dugout, the in-form U.S. side rallied to compete in their second game of the day, which was the completion of Thursday's rain-postponed duel with Canada.

    Though the Canadians had taken a one-run lead before the downpour came, they were whitewashed 8-0 by the Americans and suffered their first defeat.

    "The rain really helped us. It gave us a chance to regroup and it really worked to our advantage," commented Stacey Nuveman, the American catcher after the lop-sided game.

    In the opening game of the day, Jennifer Yee's solo homer to gift Canada the third consecutive victory and dampen the host's dream to grab a medal at softball's last Olympic show.

    "The home run was the turning point. My young players became more and more nervous then and couldn't settle down to hit ball despite faced with the golden chance," said Chinese head coach Wang Lihong.

    With a won-lost record of 2-2, China will face world number two Japan on Saturday and need at least two wins in the following three games to book a berth for the finals.

    Chinese softball players made the history by grabbing a silver medal at the Atlanta Olympics in 1996, when the sport was first introduced to the Olympic program. In the following Sydney and Athens Games, the Chinese women narrowly missed a podium finish.

    Beijing Olympics will see the final show of the sport, as it has been voted out of the 2012 London Games.

    In other two games, Australia outscored Chinese Taipei 3-1 and Venezuela thrashed the Netherlands 8-0 in five innings.

    The eight teams will play in a round-robin format at the preliminaries and the top four winners will contest for medals.

    After the fourth round competitions ended on Friday, USA (4-0), Japan (3-1), Canada(3-1), China (2-2) and Australia (2-2) will fight in the last three games for the four tickets to the finals.