Caeleb Dressel celebrates victory in the men's 50m freestyle at the Tokyo Olympics

Tokyo (AFP) - Caeleb Dressel powered to his fifth gold medal of the Tokyo Olympics on Sunday as the United States won their duel in the pool with Australia ahead of the hotly anticipated men’s 100m showdown on the track.

Elsewhere on day nine in Japan, home favourite Hideki Matsuyama targets golfing gold while Germany’s Alexander Zverev takes on Russia’s Karen Khachanov in the men’s tennis final.

US gymnastics great Simone Biles, struggling with a debilitating mental block, withdrew from the floor final, leaving her just one more chance of competition in Tokyo.

Dressel dominated the men’s 50m freestyle final with an Olympic-record time of 21.07sec and then returned to help the US team smash the world mark in the men’s 4x100m medley relay.

He also won the 100m freestyle, the 100m butterfly and the 4x100m freestyle relay earlier in the Games at the Tokyo Aquatics Centre.

Emma McKeon grabbed her fourth gold and seventh medal of the Games when she helped Australia to the women’s 4x100m medley relay crown, just 40 minutes after winning the 50m freestyle.

She is just the second woman to win seven medals at one Olympics after Ukrainian gymnast Maria Gorokhovskaya in 1952.

America’s Robert Finke touched first in the men’s 1500m freestyle to make it a distance double after winning the 800m earlier in the meeting.

Australia's Emma McKeon won seven medals at the Tokyo Olympics

Dressel, 24, failed to get close to matching Michael Phelps’ eight-gold haul in at the 2008 Beijing Games but he leaves Tokyo with his position unchallenged as the biggest name in the sport.

The American, who also won two relay golds at the Rio 2016 Games, set Olympic records in both the 50m and 100m freestyle and smashed his own world record in the 100m butterfly.

The United States ended with 11 golds in the pool, two ahead of fierce rivals Australia. Britain were third with four.

- Bolt crown up for grabs -

Later on Sunday, Usain Bolt’s Olympic 100m crown is up for grabs on the second day of action in the cavernous, spectator-free Olympic Stadium.

The pandemic-postponed 2020 Games are the first since Athens 2004 to be held without Jamaican sprint king Bolt, who retired in 2017 after winning the 100m-200m sprint double in Beijing, London and Rio.

The race looks wide open if the first round is anything to go by. American Trayvon Bromell, who owns the fastest time this year of 9.77sec, only scraped through as a fastest loser after finishing fourth in his heat.

In the morning session, China’s Gong Lijiao lived up to her pre-Olympic form by winning gold in the women’s shot put, denying New Zealand veteran Valerie Adams a third successive gold.

Gong managed a personal best of 20.58 metres on her sixth and final attempt, having led the competition from her opening effort of 19.95m.

Japan's Hideki Matsuyama is among the leaders heading into the final round of the golf

The golf competition is set for a thrilling climax at the Kasumigaseki Country Club, with a clutch of stars including Xander Schauffele, US Masters champion Matsuyama and Britain’s Paul Casey all in the mix.

“I’m going to focus on having fun and trying to play well,” said Matsuyama, who is playing in the final group of his home Olympics.

With Biles taking a back seat due to mental health issues, freshly crowned all-around champion Sunisa Lee goes for uneven bars gold as the apparatus finals begin.

Biles’s withdrawal from the floor final leaves just Tuesday’s beam as she wrestles with the “twisties”, which leave gymnasts unable to orientate themselves in mid-air.

“Simone has withdrawn from the event final for floor and will make a decision on beam later this week. Either way, we’re all behind you, Simone,” USAG tweeted.