Unheralded Italian sprinter Lamont Marcell Jacobs stormed to a shock gold in the Olympic 100 metres on Sunday after Caeleb Dressel collected his fifth swimming gold medal of the Games.

Jacobs crossed the line in a European record of 9.80sec at the Olympic Stadium to succeed retired Jamaican legend Usain Bolt as champion of the blue riband event of the athletics programme.

Fred Kerley of the United States took silver in 9.84sec and Canada's Andre de Grasse collected bronze in 9.89sec.

The fastest man in the world this year, American Trayvon Bromell, was eliminated in the semi-finals.

Caeleb Dressel celebrates victory in the men's 50m freestyle at the Tokyo Olympics
Caeleb Dressel celebrates victory in the men's 50m freestyle at the Tokyo Olympics AFP / Attila KISBENEDEK

Jacobs had not even broken 10 seconds until this year.

"It was my childhood dream to win an Olympic Games and obviously a dream can turn into something different, but to run this final and win it is a dream come true," the Texas-born Italian said.

Jacobs credited improvements in training, diet and mentality for his progression this season.

"I really work hard with my mind," he told AFP. "Because when I was arriving at the big moment my legs don't work too good. Now my legs go really good when it's a big moment."

Australia's Emma McKeon won seven medals at the Tokyo Olympics
Australia's Emma McKeon won seven medals at the Tokyo Olympics AFP / Attila KISBENEDEK

On the final day of the swimming, the United States won their epic duel in the pool with Australia.

Dressel dominated the men's 50m freestyle final, setting a new Olympic record of 21.07sec, and then returned to help his team smash the world mark in the men's 4x100m medley relay.

Japan's Hideki Matsuyama is among the leaders heading into the final round of the golf
Japan's Hideki Matsuyama is among the leaders heading into the final round of the golf AFP / YOSHI IWAMOTO

The other undoubted swimming star of the Games was Emma McKeon, who finished with four golds to become the first woman to win seven swimming medals at a single Olympics.

McKeon provided a triumphant finish when she helped Australia to the women's 4x100m medley relay crown, less than 40 minutes after winning the 50m freestyle.

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

The United States ended with 11 golds in the pool, two ahead of fierce rivals Australia, whose nine golds marked their best ever showing.

Xander Schauffele in action during the fourth round of the Olympics golf competition
Xander Schauffele in action during the fourth round of the Olympics golf competition AFP / Kazuhiro NOGI

Dressel, 24, didn't get close to matching Michael Phelps' eight-gold haul at Beijing 2008 but he joins just four other swimmers with at least five wins at a single Games.

"I'm proud of myself," said the American, who also won two relay golds at the 2016 Rio Games. "I think I reached what my potential was here at these Games."

McKeon, 27, became just the second woman to win seven medals at one Olympics in any sport, after Ukrainian gymnast Maria Gorokhovskaya in 1952, and is now Australia's most successful Olympian, with five gold medals and 11 overall.

"I look at the athletes that have gone before me and have been so impressed and inspired by what they've done but I've never been into the stats and medal counts," she said.

"But to be in that kind of company, it's an honour and I know I've worked hard for it."

In other athletics action, triple jumper Yulimar Rojas of Venezuela produced a new world record with her last leap of 15.67m, smashing the previous best of 15.50m set by Ukraine's Inessa Kravets 26 years ago.

"I am lost for words, I can't describe this feeling and this moment," Rojas said.

Qatari high jumper Mutaz Essa Barshim and Italy's Gianmarco Tamberi shared the high jump gold after both cleared 2.37m.

An overjoyed Tamberi was on hand for an emotional embrace with compatriot Jacobs after his victory.

US golfer Xander Schauffele held his nerve at the Kasumigaseki Country Club to see off Slovakia's Rory Sabbatini by one shot to take the gold medal in the men's competition.

The American world number five finished on 18-under par 266 after carding a 67 while veteran Sabbatini shot a stunning, course-record 10-under-par 61. Behind them, there was a seven-man playoff for bronze, won by C.T. Pan of Taiwan.

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

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.

Britain's Charlotte Worthington won the first BMX freestyle gold in Olympic history, while Australia's Martin Logan took the men's title.

Olympics chiefs sweated over the marathons and race walks, with temperatures at the race venue in Sapporo, north of Tokyo, expected to hover between maximums of 31 and 34 degrees Celsius (88 to 93 degrees Fahrenheit) over the next week.