She defeated German Kerstin Thiele in a tense final Wednesday in the 70-kilogram category of Olympic judo — a match marked by aggressive grabbing and pulling that sometimes resembled a schoolyard fight.
Decosse won a silver at Beijing and is a triple world champion. She dropped to the mat on her back clutching her face after winning and had to be coaxed to her feet by the referee for the official announcement that she had won.
The 30-year-old was in top form Wednesday, winning several of her fights with a match-ending ippon. One bout ended in just 10 seconds after Decosse flipped her opponent flat on her back.
Decosse said she knew she would win when she saw Thiele in tears after her semifinal. "I knew she was happy just to be in the final but for me, I wasn't there to be in the final," she said. "I wanted to win and I did."
Her medal is the first judo gold France has won at the London Games. It has three bronzes.
The women's bronze medals were won by Yuri Alvear of Colombia and Edith Bosch of the Netherlands.
It was Colombia's first Olympic judo medal. Alvear said the president called to congratulate her on her victory just as the medal ceremony was just about to begin. "I told him I'd call him back," she said.
In the men's 90-kilogram division, Song Dae-nam of South Korea won the gold medal, adding to the country's judo haul. South Korea had already won one gold and one bronze this week.
Song defeated Cuban Asley Gonzalez in a closely contested final that went into overtime. Both players were on the defensive for much of the bout, until Song used speedy footwork and dropped low to give him an edge in throwing Gonzalez for the win.
Earlier in the day, Song knocked out one of the competition's favourites, Japanese fighter Masashi Nishiyama, the world No. 3. Nishiyama later won a bronze.
The 33-year-old Song came in 17th at the world championships last year and was viewed by many as an outsider, a characterization Song disputed. "All athletes who come to the Olympics are capable of winning," he said.
The other bronze medal was won by Ilias Iliadis of Greece, who went into the division as world No. 1 and was favoured to win.
For Japan, it was another day of disappointment. Nishiyama's bronze was the only medal of the day. The country that invented the martial art has managed only one gold, two silver and three bronze medals.
Japan had hoped to reclaim its dominance of the sport after winning four golds in Beijing in 2008, a drop from the eight it claimed in Athens in 2004.
Nishiyama said he couldn't explain why Japan hadn't won more golds, but that there was no one to blame other than the Japanese themselves.
Decosse said other countries had simply become better at judo. "(Japan's) supremacy in judo has come to an end," she said.
"The fact is Japan is not doing very well at these Olympics," Nishiyama added. "We have to take advantage of it."