Keely Hodgkinson made a winning start to her bid for world gold and 100m bronze medallist Zharnel Hughes also won his 200m heat in Budapest.
Olympic and world 800m silver medallist Hodgkinson, 21, took victory in her heat in one minute 59.53 seconds.
Hughes, who on Sunday became the first British man to make a world 100m podium for 20 years, won in 19.99 secs.
Dina Asher-Smith, Daryll Neita and Bianca Williams all also progressed in the women’s 200m heats.
European champion Hodgkinson moved clear in the closing stages to qualify comfortably for Friday’s semi-finals.
Team-mate Jemma Reekie (1:59.71) went through from her heat in second place but Isabelle Boffey (2:01.40) missed out.
Hodgkinson’s expected rivals for gold – American Athing Mu (1:59.59) and Kenyan Mary Moraa (1:59.89) – both qualified with wins.
“I’m in really good shape and I am ready for any type of race,” Hodgkinson said.
“I need to trust my race and my ability, I’m not really focusing on anyone else.”
Britain’s Josh Kerr and Neil Gourley will compete for a medal in the men’s 1500m in Wednesday’s evening session (20:15 BST), which also sees Molly Caudery contest the women’s pole vault final (18:30).
All smiles for Hughes as attention turns to 200m
Fresh from claiming his first individual global medal, Hughes could afford to take several looks to either side in an efficient victory.
Evidently satisfied with his performance, he smiled to himself as he cruised across the line.
“It was a stroll, I felt like I was warming up,” Hughes said. “I feel inspired. The 100m woke me up. It has made me hungry to go out and win another medal.”
The British record holder’s sub-20 second run proved the fastest qualifying time for Thursday’s semi-finals, followed by Olympic and world silver medallist Kenny Bednarek (20.01) and reigning champion Noah Lyles (20.05) – winner of 100m gold three days ago.
Asher-Smith was left puzzled and disappointed by her performances as the women’s 100m concluded on Monday, saying she could not feel her legs in the semi-final before placing eighth in the final.
The 2019 200m world champion faced no issues in winning her heat in 22.46 secs as she aims to respond in her favoured event.
Neita (22.39), who was unable to reach the 100m final, and Williams (22.67) joined Asher-Smith in achieving automatic qualification with their respective second and third places.
American Sha’Carri Richardson marked her return to the track following her 100m triumph by clocking 22.16 secs to set the fastest time of the round.
Elsewhere, Sweden’s pole vault world record holder Armand Duplantis made three successive first-time clearances from 5.55m up to 5.75m to qualify for Saturday’s final.
Wednesday could prove a golden night for Norway, with reigning Olympic champions Jakob Ingebrigtsen and Karsten Warholm going for gold in the men’s 1500m and 400m hurdles respectively.
The scheduled women’s 5,000m heats were moved to the afternoon session because of extreme heat in Budapest, where temperatures are above 30C.
