Chicago - Lilly King set an American record in the 50m breaststroke on Thursday at the US Swim Championships in Indianapolis, a qualifying meet for next month's World Championships in Budapest, Hungary.
King won the final in 29.66 seconds, beating runner-up Katie Meili by 0.45 of a second and breaking the old US mark of 29.80 set by Jessica Hardy in 2009.
Three other sprint races produced meet records for winners who booked their trips to worlds.
Justin Ress won the 50m backstroke in 24.41, 0.11 under David Plummer's old meet mark from 2013.
Kevin Cordes, coming off a 200m breaststroke title on Wednesday, won the 50m breaststroke in 26.88, shaving 0.01 off the meet record he set in preliminaries.
Hannah Stevens won the 50m backstroke in 27.63, .05 under Rachel Bootsma's mark from 2013.
Caeleb Dressel, who already won the 50m butterfly crown, captured the 100m butterfly title in 50.87, 0.43 ahead of Tim Phillips.
Kelsi Worrell, also coming off a 50m butterfly title, won the 100m butterfly crown in 57.38 with Sarah Gibson second, 0.58 adrift.
Chase Kalisz, last year's Rio Olympic runner-up in the 400m individual medley, took the US crown in the event in 4:06.99 with fellow Olympian Jay Litherland second in 4:09.31.
Leah Smith set a personal best in the women's 400m IM to win in 4:33.86 with Elizabeth Beisel second in 4:38.55.
Five-time Olympic champion Katie Ledecky, who was idle on Thursday, has already won the 200m and 800m freestyle titles and seeks her third US crown on Friday in the 400m freestyle. She goes for the 1 500m freestyle title on Saturday.
Ledecky captured 200m, 400m and 800m freestyle Olympic gold last year in Rio - defending the 800m crown she won in London - and helped the US women's 4x200m relay win as well.
Ledecky won the world 400m, 800m and 1 500m freestyle titles and shared in a 4x200m free relay win in 2013 in Barcelona then defended those crowns while adding the 200 world title in 2015 at Russia.
Top finishers from Thursday's finals on the third day of the US Swim Championships at Indianapolis, Indiana, a qualifying meet for next month's World Championships in Budapest (all distances meters):
50m backstroke: 1. Justin Ress 24.41 seconds, 2. Ryan Murphy 24.64, 3. Matt Grevers 24.67
50m breaststroke: 1. Kevin Cordes 26.88, 2. Andrew Wilson 27.18, 3. Cody Miller 27.24
100m butterfly: 1. Caeleb Dressel 50.87, 2. Tim Phillips 51.30, 3. Jack Conger 51.33
400m individual medley: 1. Chase Kalisz 4:06.99, 2. Jay Litherland 4:09.31, 3. Gunnar Bentz 4:11.66
50m backstroke: 1. Hannah Stevens 27.63, 2. Kathleen Baker 27.69, 3. Ali DeLoof 27.89
50m breaststroke: 1. Lilly King 29.66, 2. Katie Meili 30.11, 3. Molly Hannis 30.24
100m butterfly: 1. Kelsi Worrell 57.38, 2. Sarah Gibson 57.96, 3. Mallory Comerford 57.97
400m individual medley: 1. Leah Smith 4:33.86, 2. Elizabeth Beisel 4:38.55, 3. Brooke Forde 4:39.19