WATCH: Cameron van der Burgh breaks world record in Kazan heats
South Africa's Cameron van der Burgh became the first male swimmer to set a world record at this year's world championships on Tuesday, lowering his own 50 metre breaststroke mark to secure a semi-final berth in style.
The 26-year-old defending champion touched the wall in 26.62 seconds to join Sarah Sjostrum, Katie Ledecky and Katinka Hosszu's world record efforts during the first two days of competition in Russia.
However, Van der Burgh's time in the breaststroke sprint, a non-Olympic event, also matched British rival Adam Peaty's standard set at last year's European championships.
In Berlin, Peaty initially broke Van der Burgh's world record of 26.67, but FINA, the sport's governing body, has yet to ratify the time due to an administrative error in testing the Briton for blood doping agent EPO (erythropoietin).
As it was, Peaty qualified second fastest in 26.68 on Tuesday, having edged Van der Burgh out for gold in a thrilling finale to the men's 100m breaststroke the previous evening.
"I am really happy after the bittersweet disappointment of not having the luck of the touch," Van der Burgh told reporters.
"We are all so close, it won't be a two-horse race and the final will be great. This record will not stand, either if it's by me, Adam or Damir (Dugonjic 26.70)."
In the women's 200m freestyle, Ledecky cruised to victory in her morning qualification heat, the American teenager posting the fastest time ahead of a grueling schedule later on Tuesday.
The 18-year-old high school graduate, who won the women's 400m freestyle title on Sunday, will be favourite to add the women's 1500m freestyle title, before lining up in the 200m freestyle semi-finals around 20 minutes later.
The high quality race is shaping up to be one of the most hotly contested finals of the week. Ledecky won her heat in one minute 55.82, with Hosszu qualifying 0.50 seconds behind and America's Missy Franklin lying in third.
"I slept well last night, the 200m is a different animal... it's more of a sprint for me," Ledecky said.
Meanwhile, Conor Jaeger qualified fastest for Wednesday's men's 800m final with a time of seven minutes 44.77. Defending champion Sun Yang of China recorded the sixth fastest time, 3.10 seconds down on the American.
Laslo Cech, of Hungary, advanced to the men's 200m butterfly semi-finals as the fastest qualifier.
Finals scheduled for later on Tuesday also include the men's 200m freestyle, men's and women's 100m backstroke and women's 100m breaststroke.