The wind was virtually non-existent in the morning in the American city's Regatta Park before improving in the afternoon.

Onishi triumphed in the sole race possible in the women's R:SX class to finish in front of Israel's Noga Geller and Hélène Noesmoen of France.

Croatian brothers Sime and Mihovil Fantela also made a good start in the 49er class.

They won the second race after finishing fifth in the first to take an early lead over defending champions Diego Botin and Iago Lopez Marra of Spain.

Mads Emil Stephensen Lübeck and Nikolaj Hoffmann Buhl of Denmark lie third.

A total of 543 sailors from 50 nations are competing in the Florida city.

All 10 Olympic classes are being contested.

Japan also lead after the opening race in the men's 470 event.

Naoki Ichin and Hasegawa Takashi crossed first to lie in front of British duo Luke Patience and Chris Grube.

Nikolaus Kampermühler and Thomas Czajka of Austria lie third.

Action will continue tomorrow.