Fiji captain Osea Kolinisau led the defending Sevens World Series champions in a ruthless start to rugby's return to the Olympics.

He got the first of five first-half tries, two converted, for a 29-0 lead that a leaden-footed Britain never looked like matching.

In a sevens masterclass, the Fijians avoided contact and the long-pass game, putting faith in coach Ben Ryan's "no reward without risk" gameplan of offloading to keep possession.

The islanders starved the British of the ball, competing successfully at every re-start and refusing to panic on the few occasions they threatened.

The outstanding Kolinisau got his side on the scoreboard, riding Tom Mitchell's tackle to touch down in the corner.

Jerry Tuwai followed soon after with Britain's defence failing to cope with the Pacific islanders' off-loading brilliance.

Jasa Veremalua, Leone Nakarawa and Vatemo Ravouvou all crossed in quick succession, two conversions from skipper Kolinisau handing Fiji the mammoth 29-0 half-time lead.

Another Semi Kunatani offload saw blockbusting Toulon winger Josua Tuisova go in under the posts, the British defence left clueless at the panic-free deftness of their rivals.

Dan Norton claimed a consolation try but it was all about Fiji, their bench left in tears as the game progressed. Viliame Mata rubbed salt into the wounds with a seventh final try to the delight of the partisan crowd that included IOC president Thomas Bach, Fijian Prime Minister Frank Bainimarama and Princess Anne.

Fifteen a side rugby was played at the 1924 Olympics but the sport is now seeking a permanent place with its seven a side version.

The bronze medal match proved to be one too many for Japan, shock winners over fancied New Zealand in their opening pool match, as South Africa crushed them 54-14.

A Rosko Specman hat-trick and a Cecil Afrika double proved the bedrock for the convincing victory for the reigning Commonwealth champions and second seeds in Rio.

Springbok international centre Juan de Jongh notched up South Africa's first try before Specman glided through some soft midfield defence as a rout threatened.

But Japan fired back through skipper Yusaku Kuwazuru, who muscled over from close range, before Specman was again the beneficiary of a long mispass from Afrika as the Blitzboks flooded the Japanese defence.

Kazuhiro Goya opened the scoring in the second period, but Afrika then notched up a quick brace before Justin Geduld, Specman with his third and Cheslin Kolbe rounded out a big score in a loose match between two tired-looking sides.