Tiffeny Milbrett's last minute header from Mia Hamm's cross had forced the extra period after Norway had taken a scarcely deserved lead in the 77th minute.
Dagny Mellgren's golden goal lived up to its name to give Norway the gold medal in the Olympic women's football tournament on Thursday in a closely fought contest with old foes the United States.
Mellgren - a second-half substitute - chested the ball down in the 12th minute of the extra period before firing a shotbeyond US goalkeeper Siri Mullinix.
The result confirmed the Scandanavians' position as the nemisis of the United States, who had previously been unbeaten in international competition since losing to Norway in the semi-final of the 1995 World Cup.
"We can claim to be the best side in the world now," said Norway coach Per-Mathias Hagmo.
"We have now beaten the US four times this year and China three times."
Tiffeny Milbrett's last minute header from Mia Hamm's cross had
forced the extra period after Norway had taken a scarcely deserved
lead in the 77th minute.
Mullinix was at fault, colliding with defender Joy Fawcett when dealing with a cross to allow Ragnhild Gulbranden's header to fly into an empty net.
But the Norwegian's real hero was goalkeeper Bente Nordby, who made a string of second-half saves to keep the scores level.
"You need matchwinners and Bente is a match-winner," said Hagmo
"We were the better time in extra-time, we were the ones trying to create chances. We knew the US would tire and I told the players that it was our day."
US coach April Heinrichs paid tribute to the battling qualities of the Norwegians, despite seeing her team dominate the game and still end up having to settle for consolation silver medals.
"We have a deep respect for the Norwegians winning mentality - they are champions," she said.
"They kept their game plan simple and never gave up.
"We walked off the field with tears in our eyes but I am incredibly proud of my team. We played some magnificent football tonight. We only have silver but our game was golden."