In a bruising match between two fierce rivals, the Americans appeared to have the win wrapped up in regulation after Australia captain Kate Gynther's shot rattled the crossbar in the closing seconds.
But with one second on the clock, U.S. coach Adam Krikorian called a time-out without his team having possession of the ball — an automatic penalty. Australia's Southern Ash converted the ensuing penalty to level at 9-9 and force extra time.
"We looked at each other and said 'we've been through this before,'" Steffens said of the team huddle ahead of overtime. "Nothing's going to affect us. We're going to be the team that finishes this. We knew that whatever it came down to, we're going to keep fighting."
And in extra time they did just that, with Steffens leading the way on the offensive end.
The 19-year-old, who raised her tournament scoring tally to 16 goals, put the U.S. ahead halfway through the first of two three-minute overtime periods with a skip shot, setting of chants of "USA! USA!" in the packed water polo arena at Olympic Park. Kami Craig then slotted home from close range to finish off the scoring and give the Americans another shot at their first gold medal in the event.
Even on a team with two four-time Olympians — Brenda Villa and Heather Petri — playing in their last games, there may have been no one more relieved on the U.S. bench than Krikorian.
"I was feeling horrible. There's thoughts that go through your mind. Man, I might have blown this one," he said of his time-out call. "It's all a bit of a blur, but ultimately I made a big mistake ... To be honest, after it happened, it took me a couple of minutes to take a deep breath and realize what I had done and get out of the funk."
But the team's response to his mistake, he said, was evidence of just how much the squad has developed since he took over in 2009.
"When you mess up, you've got to own up to it. They came over and I said, 'My bad.' This is not going to stop us," he said. "We've made mistakes before and we've overcome a lot of adversity over the last three and a half years so one stupid call by the coach isn't going to affect the team's performance."
The U.S. advances to Thursday's final, where it will face either Spain or Hungary, who play in the other semifinal later Tuesday.
The U.S., long one of the world powers in women's water polo, has medaled in women's water polo at every Olympics since the game debuted in 2000, but it has never won gold. It earned silver in Sydney, bronze four years later in Athens and then silver again in Beijing in 2008.
For Australia, the loss was doubly painful, coming four years after they lost to the U.S. 9-8 in the semifinals at the Beijing Olympics.
"It's pretty devastating after four years of hard work," Ash said. "We never gave up, but it just wasn't there at the end. Credit to the USA. They put up a very good fight."
The U.S. advances to Thursday's final, where it will take on a Spanish side that has made the most of the country's first appearance in women's Olympic water polo. The two teams drew 9-9 in the preliminary stage.
Spain never trailed in its semifinal clash Tuesday night Hungary, jumping out to a 4-1 lead early in the second quarter behind two goals from Espar Llaquet. The Hungarians clawed back to within a goal on several occasions, but Spain always managed to find an answer to restore its two-goal cushion.
"We wanted to play and win every single match with the objective of making it to the final, and we've done that," captain Jennifer Pareja said. "We started a four-year project, brought in a new coach and put the emphasis on young players with the goal of making the Olympics, and now we're in the final."
Hungary will take on Australia in the third-place game, which will be a rematch of the bronze medal match four years ago in Beijing that Australia won in a penalty shootout.
Hungary and Australia will play in Thursday's third-place game, which will be a rematch of the bronze medal game four years ago in Beijing that Australia won in a penalty shootout.
Ryan Lucas can be reached on twitter at www.twitter.com/relucasz