Ress led the timings in the heats and semi-finals, and triumphed by 0.02sec over compatriot Hunter Armstrong with his time of 24.12.

However, a lengthy review by the judges led to him being disqualified for being fully underwater at the finishing line.

Ress had been ready to conduct his winners interview the news was announced to a stunned Duna Arena in Budapest, Hungary.

Armstrong was left disappointed at the decision affecting his team-mate.

"I'm happy with this meet, I swam my best times here, this time also makes me happy," he said.

"But most importantly I'm very upset that my team-mate was disqualified and hopefully Team USA's protest will be successful."

Armstrong lined up on the podium initially for the victory ceremony alongside silver medallist Ksawery Masiuk of Poland, who clocked 24.49, and Italy's Thomas Ceccon, fresh from breaking the 100m backstroke world record on Monday (June 20).

Yet there was further drama, as Ress was reinstated as the race winner, and later had his own victory ceremony to formally receive the gold medal.

"I felt every single human emotion there is in a 30 minute span, so that's fun," Ress wrote on Twitter.

Ceccon dropped out of the top three with his time of 24.51.

The controversy with regards to the first race was followed by further remarkable storylines in the remaining six swimming finals.

Lithuania's Rūta Meilutytė won her first gold medal at the World Championships for nine years with her women's 50m breaststroke victory.

Meilutytė won 100m breaststroke Olympic gold at the age of 15 at London 2012.

However, she served a 24-month suspension for anti-doping rule violations between July 2019 and 2021, missing Tokyo 2020.

Having already claimed 100m breaststroke bronze in Budapest, she ensured a triumphant return to the World Championships by winning the 50m final in 29.70.

Benedetta Pilato of Italy took silver for the second consecutive World Championships in 29.80, with South Africa's Lara van Niekerk completing the top three in 29.90.

A Championships record was then set in the men's 1,500m freestyle by Italy's Gregorio Paltrinieri.

For much of the race, he looked set to break the world record set at London 2012 by China's Sun Yang, and he was more than three seconds in the green with 150m remaining.

The world record slipped away, but his time of 14min 32.80sec was the second fastest of all time, and clinched victory by almost four seconds in front of reigning Olympic champion Bobby Finke of the US.

Finke clocked 14:36.70, while Germany's Florian Wellbrock, the Tokyo 2020 bronze medallist, came through in third in 14:36.94.

This was Paltrinieri's third victory in the 1,500m freestyle at the World Championships, adding to his gold at the Rio 2016 Olympics.

Sweden's Sarah Sjöström claimed her second victory in Budapest, triumphing in the women's 50m freestyle final.

She notched 23.98, with second-placed Katarzyna Wasick of Poland 0.20 further back.

Australia's Meg Harris and the United States' Erika Brown took joint bronze medals with their times of 24.38.

Sjöström is now within one individual medal of American swimmer Michael Phelps' all-time record of 20 at a FINA World Championships, with editions scheduled for 2023 in Fukuoka and 2024 in Doha.

Summer McIntosh claimed her second gold medal of a remarkable Championships.

The 15-year-old Canadian set a world junior record of 4:32.04 in the women's 400m individual medley, followed by an American pair of Katie Grimes in 4:32.67 and Olympic silver medallist Emma Weyant in 4:36.00.

Swimming finals concluded with the men's and women's 4x100m medley relays.

Italy won their first gold medal in a relay at the World Championships by triumphing in the men's race as Alessandro Miressi edged a battle with the US' Ryan Held on the final leg.

Thomas Ceccon, Nicolò Martinenghi, Federico Burdisso and Miressi clocked a European record 3:27.51, beating the 3:27.79 from the US.

Britain rounded off the podium in 3:31.31.

The US did claim their 17^th swimming gold of the Championships by winning the women's 4x100m medley relay.

Regan Smith, Lilly King, Torri Huske and Claire Curzan recorded a time of 3:53.78, with Olympic gold medallists Australia having to settle for second in 3:54.24.

Canada took bronze in 3:55.01.

Artistic swimming drew to a close earlier in the day at the Széchy Outdoor Pool in Budapest.

Italy's Giorgio Minisini and Lucrezia Ruggiero followed their mixed duet technical routine success with another gold in the mixed duet free event, scoring 90.9667 in the final.

Japan's Tomoka Sato and Yotaro Sato took second with 89.7333, and China's Shi Haoyu and Zhang Yiyao third with 88.4000.

Russia dominated artistic swimming at the last World Championships in Gwangju in 2019, winning nine of the available 10 gold medals.

However, they and Belarus were banned by FINA from this year's edition in Budapest due to the war in Ukraine.

The gold that they failed to win in Gwangju was the women's team highlight routine, and Ukraine successfully defended their title in the Hungarian capital.

They added to their free routine combination gold with victory in 95.0333.

Italy placed second with 92.2667, and Spain rounded off the top three in 91.9333.

The second half of the World Championships is set to include diving and open water swimming competitions.

They begin tomorrow, including men's 3m synchronised diving and five kilometres team relay open water swimming finals.