Steffens, who enters Stanford as a freshman this fall, recorded a tournament-best 21 goals to help the Americans win their first gold medal in the event and send Stanford grad Brenda Villa and Cal grad Heather Petri, who both scored, off as champions.
Team USA had two silver medals and a bronze in its collection through the first three Olympic Games to include women's water polo. Villa, age 32, and Petri, age 34, were there each time a last second goal beat the Americans. Both have said they are retiring after this Olympic Games.
Steffens, the youngest player on the team at 19, made sure her older teammates would not leave without gold again.
Mountain View native Adam Krikorian, who coached at UCLA before taking the Olympic job, was thrown into the pool afterward as the final horn sounded to send the players and USA fans into a delerium.
The game was tied at 2-2 early in the second quarter when Maggie Steffens, taking a pass from older sister Jessica Steffens, scored the goal that put the Americans ahead to stay.
That was part of a streak of seven straight goals for the U.S., which was content to run the clock out most of the fourth quarter.
Stanford senior Melissa Seidemann also scored for the Americans, who also featured Cardinal junior Annika Dries on defense.
Krikorian, who called an illegal timeout during the U.S.'s 11-9 overtime thriller against Australia that nearly cost his team, can shrug that off now as he became the first American coach to lead an Olympic water polo team, men or women, to a gold medal since 1904.
That's because his team rallied in and out of the pool. The Americans are the only country to medal in each of the four Olympic Games in which women's water polo was a sport. Of course, that didn't mean anything Thursday when players were awarded the gold.
Krikorian tried calling a timeout with one second remaining of the semifinal match. His team, however, did not have possession of the ball, which becomes an automatic penalty. Australia's Southern Ash converted the shot to tie it at 9 and force overtime.
Krikorian thought his goalkeeper, Betsy Armstrong, had control of the ball.
"Everything happened so quickly," Krikorian said. "It went through my mind that I might have blown it."
The Aussies won the gold medal in 2000 after scoring in the final three seconds of the gold medal match against the U.S.
"We looked at each other and said 'We've been through this before,'" Steffens said. "Nothing is 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."
Steffens, leading the way on the offensive end, made good on her word. She put the U.S. ahead halfway through the first of two three-minute overtime periods, with a skip shot.
"She doesn't play like a newcomer," Krikorian said.
Kami Craig added a goal to finish the scoring and give the Americans another shot at their first gold medal in the women's event.
"I was feeling horrible," Krikorian said. "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," Krikorian said. "They came over and I said, 'My bad.' This is not going to stop us. 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."
He was right. The slip turned to gold.