Gwangju - China's Sun Yang captured a record fourth 400 metres freestyle world title in an acrimonious final Sunday, before Britain's Adam Peaty produced an eye-popping world breaststroke record.
Sun pumped his fists and let out a visceral roar after a pulsating race brimming with bad vibes and capped by rival Mack Horton's refusal to join the Chinese giant on the podium after the medal ceremony in Gwangju.
"Not everyone likes me - I don't care," growled Sun when asked about Horton's snub.
"It's OK if you don't respect me personally, but at the victory ceremony - which is a sincere occasion - you should show respect to my country."
The controversial triple Olympic gold medallist slapped the water in delight, pointing to his flag-waving Chinese fans as he savoured an emotional victory over Australian Horton and his 10th world championship gold medal.
Sun's latest career milestone comes after fresh allegations in a leaked FINA doping report that claimed the Chinese giant smashed blood samples with a hammer after being visited by testers last year.
The defending champion clocked three minutes, 42.44 seconds with Horton taking silver in 3:43.17 and Italian Gabriele Detti bronze in 3:43.23 in a repeat of the 2017 podium in Budapest.
As he climbed out of the pool, Sun bellowed at the crowd before breaking down in tears.
The bad blood between him and Horton continued with the Australian refusing to take part in the traditional photo after the playing of the Chinese national anthem.
The pair have clashed in the past with the Aussie, before beating him at the 2016 Rio Olympics, calling Sun a "drug cheat" over a three-month suspension for a banned stimulant Sun said he took for a heart condition.
"I don't think I need to say anything," sniffed Horton. "I think his actions and how it's been handled speaks louder than anything I could say."
Peaty smashed his own 100 metres breaststroke world record, the Olympic champion storming home to win his semi-final in a time of 56.88 seconds - becoming the first swimmer to break the 57-second barrier and eclipsing his previous mark by more than two tenths.
The tattooed pin-up, who has not been beaten for five years over the 100 metres in major competition, turned 0.12 inside world record pace as fellow Briton James Wilby struggled to keep up.
"There's no other word except for incredible," said Peaty.
"I've been chasing that for three years now, ever since I touched that wall in Rio and I knew I could go faster."
After the tension of Sun's gold medal - the first of the eight-day pool competition - Aussie teenager Ariarne Titmus stunned American great Katie Ledecky to win the women's 400m freestyle final.
The three-time champion looked in complete control until she faded coming off the final turn, allowing Titmus to storm past her to bag her first world title.
"The time wasn't a surprise," said Titmus, who clocked 3:58.76 to beat Ledecky by more than a second
"I knew I probably had that in me but it's pretty surreal at the moment - Katie's a true champion."
A deflated Ledecky admitted: "This stings a little. I need to rebound from this, get my fight back."
Caeleb Dressel, who swept seven medals at the 2017 world championships, led the American men's 4x100m freestyle team to gold in a meet record of 3:09.06, retaining their title by almost a second from Russia in silver.
Hearing of the latest spat between Sun and Horton, Dressel said: "I'm sure there's some strong feelings there - swimming's getting intense, jeez!"
Cate Campbell anchored Australia to gold in the women's 4x100m free in the evening's final race.