Operating on very little sleep, the triple Olympic champion clocked 1 min 46.22sec the morning after winning an emotionally draining battle with Australian rival Mack Horton to capture a record fourth world championship gold in the 400m free.
American Katie Ledecky returned to the pool looking to exorcise the ghosts of her stunning defeat by Aussie teenager Ariarne Titmus on the first day of the swimming competition in Gwangju, posting the fastest qualifying mark in the women’s 1,500m freestyle.
Sun, whose 400m victory was his 10th world title, is competing under a doping cloud in South Korea after being accused by independent FINA testers of smashing blood samples with a hammer.
But he has shown no signs of stress, entering the pool deck to ear-piercing screams from his legion of adoring female fans waving Chinese flags and chanting their hero’s name.
“I ate dinner at midnight last night and went to bed at two,” Sun told reporters.
“I’m happy with my heat time after a close battle in the 400m free. The 200m is a bit of a lottery — lots of people have a chance to win gold, but I’ll give everything.”
His time was pipped by Briton James Guy’s 1:46.18 in the final heat, but the controversial Sun — the reigning Olympic champion in the 200m free — remains the strong favourite to retain his world title.
‘She looks angry’
Three-time defending champion Ledecky logged an easy 15:48.90 in the 1,500m heats after fading badly in the 400m final as Titmus lurked.
The Australian’s coach Dean Boxall warned that the 18-year-old had awoken the beast.
“Ledecky looks pissed off, angry,” he told Australian media. “She’s going to come back — she’ll be like a caged tiger coming out.”
World and Olympic champion Lilly King, who last week blasted FINA’s “sketchy” doping controls, pipped Russian rival Yulia Efimova to the fastest time in the women’s 100m breaststroke heats by almost half a second.
The American, who refused to shake Efimova’s hand after beating her at the 2016 Rio Olympics because of a suspension the Russian had served for taking a banned steroid, clocked 1:06.31 to ease into the evening’s semi-finals.
“The athletes have to stand up for themselves,” insisted King after her heat swim.
“It’s definitely a start if these guys are taking a stand against doping.”
Title holder Xu Jiayu topped the men’s 100m backstroke heats, the Chinese star touching in 52.85 with Olympic champion Ryan Murphy and Commonwealth gold medallist Mitch Larkin also safely through.
Canada’s Kylie Masse began the defence of her women’s 100m backstroke title with a comfortable 58.91.
Later on Monday, Britain’s Adam Peaty targets his second world record in two days in the 100m breaststroke final while Swede Sarah Sjostrom can become the first female swimmer to win the same world title five times in the 100m butterfly.