The American women's water polo team got its stiffest challenge of the 2012 Olympics on Tuesday against previously undefeated Australia in a semifinal match. But after a controversial call got the Aussies into extra time against the U.S., Team USA moved on, 11-9, with a strong overtime period.

Maggie Steffens and Kami Craig both scored in the first three-minute extra time period to put the U.S. up by the final score, and the Americans allowed no shots on target in the second extra time, holding off the only team that had been undefeated in the pool in Olympic play.

The win guarantees the U.S. a medal in the event, making four in all four Olympics with water polo competitions since 2000. Team USA will be angling for the nation's first gold in the event on August 9, when it meets the winner of the second semifinal between Hungary and Spain.

The U.S. would not have had to go to extra time to vanquish Australia had it not been for a call awarding the Aussies a penalty shot with one second left in the second half. Ash Southern converted that, sending the match to extra time.

For more on the Olympics, check out SB Nation's London 2012 Olympics Hub. For more on Olympic water polo, follow the 2012 Olympic water polo section.