For the fifth time in as many Olympics the sport has been played, the U.S. softball team will be playing for a gold medal.Amanda Chidester’s two-run, walk-off single in the bottom of the eighth inning propelled the U.S. past Australia 2-1 Sunday at Yokohama Baseball Stadium in Yokohama, Japan. Monica Abbott struck out 13 while allowing just three hits for the U.S., while Tarni Stepto scattered five hits for Australia.By virtue of winning its first four games of pool play, the top-ranked Americans clinched a shot at their fourth gold medal Tuesday. They will play either second-ranked Japan (3-0) or third-ranked Canada (2-1) — who play one another later Sunday — for gold. The format for these Olympics is the top two teams in pool play will battle for gold, while the third- and fourth-place teams vie for bronze.The U.S. wraps up pool play Monday against Japan, who beat the Americans 3-1 for the gold medal in the 2008 Beijing Olympics, the last time softball was played in the Games.Offense has been hard to come by in the Olympics for the U.S. The same was true against Australia. Center fielder Haylie McCleney led off the bottom of the first inning with a triple to right field but was thrown out at the plate two batters later. The U.S. had two on with one out in the third, but a double play erased that threat. Two more runners reached in the fifth, but Australia got out of it unscathed.Abbott, one of two returning Olympians on the U.S. team (along with fellow pitcher Cat Osterman), had to work out of one jam, which came in the sixth inning. Australia put the first two runners on before Abbott got back-to-back pop outs. Abbott’s second walk of the inning loaded the bases, but she struck out pinch-hitter Michelle Cox for her 10th punchout of the game.With the score tied 0-0 the game moved to extra innings. In the top of the eighth — which started with a runner at second base — Abbott uncharacteristically walked three batters, forcing in a run. It was the first allowed by the U.S. in the Tokyo Olympics.With Ally Carda pinch-running at second to start the bottom of the inning, McCleney singled to shortstop and Janie Reed bunted the runners to second and third. Chidester then drilled the first pitch she saw from Stepto into the left-center gap, easily scoring Carda and McCleney and sending the U.S. to the gold-medal game.