RIO DE JANEIRO (AFP) - Judoka Rafaela Silva upset world number one Sumiya Dorjsuren to win hosts Brazil's first gold medal of the Rio Games on Monday.

Silva, who grew up in Rio's notoriously violent City of God neighbourhood, sunk to her knees after winning the under-57kg final with a half point waza-ari score from a leg reap counter attack, before leaping into the stands to hug her supporters.

London champion Kaori Matsumoto of Japan took bronze alongside five-time European champion Telma Monteiro of Portugal.

Silva continued Brazil's recent ascension in women's judo, adding to the first ever gold medal won by the team in London four years ago through Sarah Menezes at under-48kg.

The rise has been meteoric since Ketleyn Quadros won Brazil's first Olympic women's judo medal in Beijing in 2008, taking under-57kg bronze.

Quadros's international career was cut short by the emergence of Silva, 24, in 2011 when she took silver medals at the world championships and Pan-American Games.

Silva, ranked only number 11 in the world, had upset the world number two Kim Jandi of South Korea in her second contest.

She needed a period of golden score to get past Romania's Corina Caprioriu in the semi-final after a nervy bout that remained on tenterhooks throughout.

Silva scored the winning waza-ari after cleverly changing the direction of her attack from a hip throw to the front into a leg sweep to the rear.

In the other semi-final, Dorjsuren had accounted for Japanese darling Matsumoto with a slick shoulder throw from her knees to score the maximum ippon.