FUKUOKA, Japan, July 25, 2023 (BSS/AFP) - French star Leon Marchand was back in action at swimming's world championships on Tuesday, easing through his 200m butterfly heat two days after smashing Michael Phelps's last remaining world record.

Marchand won the men's 400m individual medley on the opening night of competition in Fukuoka, coming home in a staggering time of 4min, 02.50sec.

That took more than a second off Phelps's benchmark of 4:03.84, which had stood since the 2008 Beijing Olympics and was the longest-held world record in swimming.

Marchand returned to the pool for the 200m butterfly heats, qualifying seventh-fastest in a time of 1min, 55.46sec.

"The goal was to expend as little energy as possible, without taking too many risks in qualifying, which he did very well," said Denis Auguin, the chief of the French team delegation.

"He was very relaxed this morning. We had a lot of laughs over breakfast."

Marchand came into the competition as the defending champion in both the 200m and 400m IM.

He will compete in the 200m butterfly semi-finals later on Tuesday but Auguin said his participation in the 200m breaststroke was still up in the air.

"I'm not sure the decision has been made," he said.

"There are several options, it will also depend on how fresh he is. He's in good shape, fresh and ready."

Japan's Tomoru Honda was the fastest qualifier in the 200 butterfly, coming home in 1:54.21.

Spain's Arbidel Gonzalez was second on 1:54.99, followed by Poland's Krzysztof Chmielewski on 1:55.02.

- Titmus back in action -

Australia's Ariarne Titmus also got back to work after winning an epic showdown in the women's 400m freestyle on the opening night.

Titmus dominated rivals Katie Ledecky and Summer McIntosh to win the title and reclaim her world record in a time of 3min, 55.38.

Titmus was back in action in the 200m freestyle heats, finishing third-fastest in 1min, 56.20sec.

Australian Mollie O'Callaghan was quickest on 1:55.68, followed by Canada's McIntosh on 1:55.88.

The 16-year-old McIntosh went into the 400 freestyle as the world record-holder but missed out on a medal after finishing fourth.

China's Qin Haiyang swam the fastest time in the men's 50m breaststroke heats, the morning after claiming his country's first gold medal of the championships.

Qin won the 100m breaststroke on Monday and was later joined on the podium by countrywoman Zhang Yufei, who took gold in the 100m butterfly.

That helped the Chinese team banish the memory of last year's world championships in Budapest, where they won only one individual swimming gold.

Qin clocked 26.34sec in the 50m breaststroke heats, followed by Italy's Nicolo Martinenghi on 26.64 and China's Sun Jiajun on 26.76.

"Winning last night's medal gives me more confidence and power," said Qin.

Australia's Sam Short was the fastest qualifier in the men's 800m freestyle heats.

Short, who won the 400m freestyle title on Sunday night, came home in a time of 7min, 40.90sec.

Tunisia's Ahmed Hafnaoui, the silver medallist in the 400, was second-fastest on 7:41.97, followed by Germany's Lukas Martens on 7:42.04.