Past champions Fiji, New Zealand, England and titleholder Wales also made assured starts on an opening day when all results went as expected.
Every team made a single appearance before a sparse crowd in the 1980 Olympic venue, with the pool games to be completed on Saturday before the playoffs on Sunday.
Fiji, the only two-time winner, blew away Tonga 45-0 with Metuisela Talebula and Watisoni Votu scoring two tries each.
New Zealand, the dominant team in the annual world series but winner of its only World Cup 12 years ago, beat Canada 31-12, and England came right in the second half to account for Portugal 21-7.
Wales, the surprise champion four years ago in Dubai, downed Uruguay 33-5.
Host Russia was spanked 31-0 by South Africa, and Philippines, the only team of the 24 making its debut, was run over by Kenya 45-5.
Results Friday in the Rugby World Cup Sevens at Luzhniki Stadium:
Pool A:
Australia 21-0 Spain
France 24-7 Tunisia
Pool B:
South Africa 31-0 Russia
Scotland 19-17 Japan
Pool C:
Samoa 21-14 Zimbabwe
Kenya 45-5 Philippines
Pool D:
New Zealand 31-12 Canada
United States 26-19Georgia
Pool E:
Fiji 45-0 Tonga
Wales 33-5 Uruguay
Pool F:
Argentina 47-7 Hong Kong
England 21-7 Portugal