Unheralded swimmer Brendon Smith could claim Australia’s first gold medal of the Tokyo Olympics in what promises to be an exciting day in the pool.

The 21-year-old Victorian shot to gold-medal favourite in the 400-metre individual medley when he set an Australian record in his heat and was quickest into his final.

Smith’s stunning swim came as the host nation’s hero, reigning medley world champion Daiya Seto, flopped and failed to make the medal race.

The 400 IM is the first of three swim finals featuring Australians on Sunday, with the women’s 4x100m freestyle relay team an unbackable favourite to deliver a Sunday gold.

The relayers — and flagbearer Cate Campbell — are seeking a third consecutive OIympic title and will race after medal prospects Elijah Winnington and Jack McLoughlin contest the 400m freestyle final.

Swim veteran Emma McKeon made a slick start in her quest to join Australia’s Olympic icons and bag seven medals.

Three Australians — Shane Gould, Ian Thorpe and Alicia Coutts — have collected five medals at a single Olympics; none has won more.

McKeon is eyeing an unprecedented seven gold in Tokyo. Photo: Getty

McKeon’s bumper program began with an ominous Saturday night swim.

McKeon was equal-fastest in the 100-metre butterfly heats, dead-heating with China’s world No.1 Zhang Yufei.

Also at the Tokyo Aquatic Centre, Bronte Halligan scored three goals and Lea Yanitsas put on a goalkeeping masterclass to help Australia to a comfortable 8-5 over Canada in women’s water polo.

Australia is seeking a fourth Olympic medal and second gold after their memorable Sydney 2000 triumph.

Gymnast Tyson Bull delivered his best international performance to qualify for the horizontal bar final at the Olympic Games in Tokyo.

The Victorian, Australia’s only male representative in the artistic events in Tokyo, nailed his routine and after a small step landing his full-twisting double layout dismount, punched the air in delight.

The Kookaburras were forced to work hard for their win. Photo: Getty

In other Day One action, the world No 1 Kookaburras opened their campaign with a 5-3 win over host Japan in the men’s hockey, while the Matilda’s were beaten 4-2 in a hard-fought match against Sweden.

John Millman downed Lorenzo Musetti of Italy 6-3 6-4 in his tennis opener, and the women’s doubles pairing of Ash Barty and Storm Sanders beat Japan’s Nao Hibino and Makato Ninomiya 6-1 6-2.

Samantha Stosur lost to Elena Rybakina of Kazakstan 6-4 6-2.

Australia’s women softball team was downed 7-1 by Canada in the preliminary round, while men’s beach volleyball pair of Chris McHugh and Damien Schumann fell agonisingly short in a three-set defeat to top-ranked Berntsen Mol and Christian Sandlie Sorum of Norway.

Day Two promises to be a hectic day for Australian Olympians, who will be in action across 22 sports.

Ash Barty singles

World No.1 Ash Barty starts her Tokyo singles campaign against Spain’s Sara Sorribes Tormo while Ajla Tomljanovic is also in action.

Barty paired with Storm Sanders on Saturday to easily beat Japan in their women’s doubles opener.

Amanda Spratt will lead a high-quality Australian cycling team in the women’s road race, but the Dutch start as overwhelming favourites.

The Olyroos, coming off their outstanding opening win over Argentina, meet Spain while Jessica Fox, chasing an elusive gold medal, has her first runs in the K1 preliminaries.

Surfing and skateboarding debut as Olympic sports with the men’s and women’s surf competitions scheduled to start at Tsurigasaki Beach.

Stephanie Gilmore, Sally Fitzgibbon, Julian Wilson and Owen Wright are Australia’s surfing team.

Shane O’Neill is Australia’s skateboarding entry, with the medals to be decided on Sunday.

Boomers in action

The Boomers, after an impressive lead-up to the Games, take on Nigeria in men’s basketball.

The Hockeyroos begin their Tokyo assault against Spain and the Kookaburras, fresh from a tough 5-3 win over the host nation, play India.

Australia must stage a major upset against the United States to keep their faltering softball campaign alive, while the Sharks play Montenegro in men’s water polo.

-with AAP