Adam Peaty won the 100 metres breaststroke at the World Championships on Monday night and returned on Tuesday morning to qualify fastest in a world record over 50m.
The 22-year-old Uttoxeter swimmer set the world record of 26.42 seconds en route to winning 50m breaststroke gold in Kazan, Russia two years ago.
Peaty was optimistic of going quicker in the non-Olympic event after a halfway split of 26.50secs in the 100m, which he had also won in 2015.
He predicted "something special" and delivered - clocking 26.10 in the morning heats.
Cameron van der Burgh of South Africa was second quickest in 26.54. The 0.44 margin is huge over one length.
Peaty's 100m title was one of two gold medals for Britain on day two, with Ben Proud winning the non-Olympic 50m butterfly.
And there was the prospect of further success on Tuesday night as Duncan Scott and defending champion James Guy qualified in first and second place, respectively, for the 200m freestyle final.