The 22-year-old qualified fastest from the heats at the Duna Arena ahead of South Africa's Cameron van der Burgh (26.54) Brazil's Joao Gomes Junior (26.67).
Peaty, who retained his 100m world title on Monday in a championship record time of 57.47 seconds, said he was delighted to set the new mark in a morning swim.
"Honestly, I wasn't going out there this morning for a world record," he said.
"It's 10 o'clock and I'm very happy with that swim. That world record is two years old, so it's due another push on."
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Peaty said there could be more to come before the final on Wednesday.
"That didn't really feel like my best race, so move it on tonight, pick up a few hundredths or tenths and we'll be very happy," he said.
South Africa's Van der Burgh had come within 0.12 of Peaty's previous world record in his preliminary heat.
The former world and Olympic breaststroke champion, whose titles have been swiped by Peaty over the last three years, opted to scratch the men's 100 to focus on the 50 dash.
(Reporting by Rod Gilmour, writing by Peter Rutherford; editing by Amlan Chakraborty)
