TOKYO - Caeleb Dressel and Katie Ledecky added to the United States' gold medal haul at the Tokyo Games on Saturday while Australia picked up an incredible seventh title and Britain won the Olympics' inaugural mixed 4x100 medley relay for their fourth swimming gold.

It has been a disappointing Games so far for the U.S. swim team, whose eight golds are just half their tally from Rio, but the performances of their biggest names gave them reason to celebrate on the penultimate day in the pool.

Dressel stormed to the 100m butterfly title with a world record time of 49.45 to pick up his second individual gold of the Games. He also won gold in the 4x100 freestyle relay.

World champion Dressel beat Hungary's Kristof Milak, the gold medalist in the 200m fly, by 0.23 seconds.

The powerful American, who also won gold in the 100m freestyle, was fastest out of the blocks and never looked in danger, though Milak came back hard to close the gap down the straight.

"This is a fair result," said Milak as Dressel headed off to prepare for the 50m free heats and mixed relay medley.

"That was the maximum I could give. I am happy that Caeleb needed a world record to beat me."

After coming second best to Australia's Ariarne Titmus in the 200 and 400 free, Ledecky got her Tokyo campaign back on track on Wednesday by winning the 1,500 and on Saturday became the first female swimmer to win six individual golds, cruising home in the 800.

Taking control from the start, Ledecky increased her lead over Titmus from the 500 mark and came home more than a second ahead of her Australian rival, winning the event for a third straight Games -- another first for the American.

"She made it tough and so it was a lot of fun to race," said Ledecky.

"I just trusted myself trusted I could pull it out and swim whatever way I needed to."

Unpredictable excitement

While Titmus had to settle for silver there was plenty for Australia to celebrate with McKeown's perfectly timed swim to complete the backstroke double.

McKeown turned up the pace on the final lap of the 200m to power past Kylie Masse after the Canadian held the lead for the first 150.

The Australian won in a time of 2:04.68 with Masse 0.74 behind and McKeown's teammate Emily Seebohm taking the bronze medal.

Australia's women have now picked up six of the country's seven gold medals in the pool.

The first mixed 4x100m medley race at the Olympics delivered all the unpredictable excitement that was hoped for when it was introduced to the program.

Britain's Kathleen Dawson trailed in sixth after the first 100 as the men of the United States, Italy and China surged ahead, but individual breaststroke gold medalist Adam Peaty slashed the deficit and pulled Britain into fourth.

Peaty handed over to James Guy, who catapulted Britain into the lead with a thrilling butterfly leg where he moved past China's gold medalist Zhang Yufei to give Anna Hopkin enough space to fend off a late challenge from Australian Emma KcKeon and China's Yang Junxuan with Dressel given too much to do for the states who finished fifth.

Britain's total of four swimming golds in Tokyo is their best return in over a century.