Sophia Smith scored the winning goal in extra time as the United States beat Germany 1-0 on Tuesday to advance to the Paris Olympics women's football final.

Smith settled a close-fought but generally poor semi-final in Lyon by firing past Germany goalkeeper Ann-Katrin Berger to finally break the deadlock five minutes into extra time.

The USA, record four-time gold medallists, were also grateful to goalkeeper Alyssa Naeher for a crucial late save from Laura Freigang and now head to the French capital for the final on Saturday.

"I saw a little opening of net and I thought I've just got to put it there. It was a good feeling," Smith said of her goal.

"I had a few other chances in this game that I should have put away but sometimes one is all it takes."

Germany, who won gold in 2016, can still claim a bronze medal as they stay in Lyon for the third-place play-off on Friday.

The Germans had been the more accomplished side in normal time although quality was desperately lacking in the final third from both teams on a stiflingly hot day.

Emma Hayes's USA played at a level far removed from their clinical display in beating Germany 4-1 in the group stage in Marseille.

However, once again the quality of their attack made the difference.

"There were lots of things I didn't like in the game. I tried every situation to try to influence and affect that, but it's not about that. It's about heart and head," Hayes said.

"You have to dig something out. Our group want to create new history for themselves. They did enough to get us in the final, and that is just the next step."

This time it was Smith who was the match-winner, firing past Berger after being picked out by a Mallory Swanson through ball.

It was a third goal at the tournament for the Colorado-born forward who turns 24 on the day of the final -- her other two strikes came against Germany in the group stage.

Contrast that cutting edge with Germany, who were dealt a serious double blow ahead of the game when ill captain Alexandra Popp and the injured Lea Schueller, the two most prolific and experienced goal-scorers in their squad, were ruled out.

The Americans had chances in the 90 minutes, including from a late Lindsey Horan header that was kept out by Berger.

Swanson even had the ball in the net, although she was well offside and the flag was raised early.

But they found a way through in extra time, and Smith was then only denied a second goal by a good Berger save.

There was drama right at the death, with Naeher somehow saving at close range to deny Freigang an equaliser before Smith almost got a second.

The USA won the last of their four women's football gold medals at London 2012. They claimed bronze three years ago in Tokyo and were also silver medallists in 2000.

Germany, whose coach Horst Hrubesch was in charge of the men's team that won silver in Rio in 2016, will now hope to leave with Olympic bronze for the fourth time.