Japan's Olympic judo campaign got off to a flying start on Saturday when Tadahiro Nomura became the sport's first triple Olympic champion and compatriot Ryoko Tani also broke new ground by taking her second gold.

Nomura went into the under-60kg category as favourite to add to his titles from 1996 and 2000 but showed none of his usual brilliance in the final against awkward Georgian Nestor Khergiani.

However, he eventually prevailed by three penalty scores to one and can now retire with his name carved among the immortals of the sport so close to the heart of his country.

Nomura's path to the title was eased when his main rivals, world champion Choi Min-ho of Korea, Britain's Craig Fallon and former world champion Anis Lounifi of Tunisia, all fell by the wayside.

He beat Khashbaatar Tsagaanbaatar of Mongolia by ippon in the semi-final before going on to match his achievement of Sydney by claiming gold on the opening day of the Games -- though that final was over in just 14 seconds.

Choi bounced back from a quarter-final defeat to win bronze against Iran's Masoud Hajiakhondzadeh and Tsagaanbaatar joined him on the podium after edging out Spain's Kenji Uematsu.

Nomura's gold came 10 minutes after six-time world champion Tani had taken the women's under-48kg title.

Tani, who won in Sydney and took silver in 1992 and 1996 as Ryoko Tamura, was fighting a month after injuring her ankle but looked her normal electric self as she beat France's Frederique Jossinet by waza-ari (half-point score) in the final.

Germany's Julia Matijass dashed Greek hopes of a home medal when she beat Maria Karagiannopoulou with an inner thigh throw to take bronze.

In a scrappy encounter, China's Feng Gao snatched the other bronze from European champion Alina Dumitru of Romania by beating her by ippon in the dying seconds.