The victory ended a medal drought for Japan that dated to the 1984 games in Los Angeles, where the team also won the bronze. The Japanese join Russia with six total medals in women's volleyball, which joined the Olympics in 1964.
When Sakoda finally left the floor at Earls Court after a long celebration of the 25-22, 26-24, 25-21 win, she was swamped by photographers and well-wishers like a rock star. She bowed to her admirers.
"Quite simply, happy," she said.
Japan has won gold in women's volleyball twice, in the sport's Olympic debut in Tokyo and at the 1976 Montreal Games. The team also won silver at the 1968 and 1972 Olympics and bronze in 1984.
South Korea's best result in Olympic play was a bronze in 1976.
Kim Yeon-koung, the leading scorer in London, had 22 points for No. 15 South Korea. She finished the tournament with 207 total points.
"I believe that throughout this tournament the level of Korean volleyball has gone to the next level," Kim said through an interpreter. "There are some areas that we did well and other areas we didn't do very well. But in those areas where we struggled we will try to improve ourselves for next time and areas we did well we will try to build on."
South Korea trailed early but took a 12-10 lead in the first set on a pair of successful spikes from Kim. The Japanese pulled back ahead 21-19 on captain Erika Araki's kill. South Korea denied Japan one set point, but Japan prevailed on Sakoda's kill.
Japan jumped to an 8-1 lead in the second. The South Koreans pulled within 16-15 on Han Song-yi's block, then denied Japan set point three times and pulled even at 24. Sakoda's kill put Japan back in front before Jung Dae-young misfired a spike.
"I chose Sakoda because the past few matches she played so well," coach Masayoshi Manabe said.
South Korea rebounded to lead early in the third, but Japan tied it at 12 and took a 15-14 lead on another Sakoda kill, which was cheered by the team's rhythmically clapping fans at Earls Court.
After Sakoda's spike for the win, the Japanese dogpiled on the court. Later, they linked hands and circled the floor in a skip.
"It's unbelievable, it doesn't feel real," Araki said. "The Olympic medal is the best moment of all, this is best."
All of Sakoda's points came on kills.
"I don't do service, I don't receive much and I don't feel I'm good at that, everyone else does a wonderful job of that for me," Sakoda said through an interpreter. "I only had to worry about scoring."
The top-ranked U.S. women, who have not lost in the Olympic tournament, face No. 2 Brazil in the gold-medal match late Saturday. It's a rematch of the final at the 2008 Beijing Games, which gave Brazil its first gold in the sport.
In London, Japan was swept by Brazil in a semifinal after outlasting No. 3 China 3-2 in the quarters, upsetting a team they had never taken a set from in five Olympic meetings.
South Korea fell to the U.S. women in straight sets in the semifinals after upsetting fourth-ranked Italy in four sets in the quarters.
It was the first time two Asian teams made the semifinals since the 1988 Seoul Games.