Budapest - Gold-medal machine Katie Ledecky cruised into the women's 1 500m freestyle final from Monday's heats at the world aquatic championships to stay on course for an historic 12th worlds gold.
Ledecky was the fastest qualifier at 15 minutes, 47.54 seconds - nearly 18 seconds ahead of the field - to maintain her iron grip on the event.
"I feel good. I just wanted to have a good controlled easy swim and get a good lane for the final," said Ledecky.
The unstoppable 20-year-old already picked up two golds on Sunday night, winning the 400m title for the third championships in a row, then helping the United States win the 4x100m relay.
That left her level with Missy Franklin on a record 11 gold medals at world championships.
Ledecky is on course to win her third title - of a possible six here - in Tuesday's 1 500m final which would make her the first woman to win 12 world championship golds.
Fresh from his 400m freestyle gold medal on Sunday, Sun Yang was the fastest through the men's 200m freestyle heats into Monday's semis, but admitted feeling jaded.
"I was a little tired, I didn't do my best in the heat, but I didn't have to," said the 25-year-old Chinese superstar.
Despite his fatigue, Sun clocked 1:45.78 with Britain's James Guy, the defending world champion, just 0.44 back.
Guy is determined to make amends for a disappointing sixth in the 400m final.
"It's parked and we've done," he insisted.
"The 200m race felt so much better this morning, there was so much more control, I just feel more relaxed."
Mack Horton, who Sun defeated in the 400m final, finished 11th and 1.19 adrift.
"Obviously that was tough after yesterday, but with an evening and a bit more rest there should be a bit more," said Horton.
"It was always going to be tough backing up and trying to get into that semi, but I should be ok."
Katinka Hosszu, the Olympic champion, was the second fastest into the evening's 100m backstroke semi-finals, just 0.18 seconds behind Canada's Kylie Masse.
Hosszu refused to speak to reporters after her heat.
Hungarian media reports claim she has pulled out of the semis to focus on the 200m individual medley final - her strongest event - which comes later on Monday night.
Australia's Emily Seebohm, who won the world title two years ago in Kazan, was third fastest at 0.33 behind Masse.
In the men's 100m backstroke heats, both the Olympic champion, Ryan Murphy of the US, and Australia's Mitch Larkin, the defending world champion made it through to the evening's semis.
The strength of the women's 100m breaststroke field shone through in the heats with Olympic champion Lilly King of the USA the fastest in 1:05.20.
But both the defending world champion Yuliya Efimova of Russia, the Olympic silver medallist in Rio, and 2012 Olympic champion Ruta Meilutyte were within a second of King.
Olympic bronze medallist Katie Meili of the US and Taylor McKeown, the 200m Commonwealth champion, were also in the top five.
There is bad blood between King and Efimova, who served a 16-month doping ban until February 2015, then won the world five months later in Kazan.
Efimova won Olympic silver in Rio only after winning an appeal to be able to race, waving her finger signalling 'No 1' after winning her semi-final.
"You wave your finger 'No 1' and you've been caught drug cheating ... I'm not a fan," retorted King in Rio last year.