A walk-off single to American third base Amanda Chidester with one out in the bottom of the eighth scored two runs, leaving the Australians shattered after a brave challenge to the gold medal favourites.

It leaves Australia fourth on the standings with a 1-3 record and they must beat Mexico in their final group game on Monday to reach Tuesday's bronze medal playoff.

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Australian pitcher Marni Stepto was outstanding, striking out three batters, giving up five hits and five walks in her complete game.

But star American left-hander Monica Abbott won a classic pitchers' duel with 13 strikeouts, giving up three hits and six walks, three of which were to Porter.

After seven scoreless inning, Australia loaded the bases at the top of the extra eighth.

Left fielder Jade Wall then gave the Australians the lead when she received a walk, scoring Belinda White, before Abbott struck out Stepto to end the inning.

But with a runner starting on second base for the extra eighth inning, American Haylie McCleney led off with a single to heap the pressure on the Australians.

Janie Reed's sacrifice bunt put the runners on second and third, setting up Chidester for her game-winning walk-off hit to left field.

Australia were left to rue nine stranded runners, while the US had seven.

The Australians loaded the bases in the sixth, only for Abbott to catch pitch hitter Michelle Cook looking and strike her out to end the inning.

It was the first run that the US conceded in the tournament as they improved to a 4-0 record.

Japan are also unbeaten and their clash with the US on Monday is a likely preview of the gold medal match the following day.

Australian Associated Press