Gaffney began the morning by setting an American record of 1min 20.96sec at the Indiana University Natatorium, but she bettered her own time in the final with a world record mark of 1:19.47.

It gave her the first world record of her career.

"I’ve been eyeing the 100m backstroke world record since I moved to the Olympic Training Center in January," Gaffney said.

"I wanted to set it here in Indianapolis.

"We’ve been working on my pull a lot, which has gotten much better.

"I saw the time and knew I set the world record.

"It feels really good to start the meet this way.

"I feel like I can relax and have fun because I’ve done what I need to do."

Ahalya Lettenberger of the United States finished second in 1:23.25, while compatriot Elizabeth Marks came third in 1:23.33.

Two Pan American records were also set on the first day of the event, courtesy of the US' Gia Pergolini and Rebecca Meyers.  

Pergolini broke the continental record in the women’s 100m backstroke S13 preliminaries, clocking 1:06.61, while two-time Paralympian Meyers posted a mark of 1:00.84 in the women’s 100m freestyle S12 final.  

The former went on to win her final in 1:06.68 with Colleen Young and Madeleine Babcock completing a US podium sweep in 1:10.55 and 1:30.91 respectively.

"The race went pretty well," Pergolini said.

"It did hurt the last 50 meters, but it’s my best time in a long time.

"We’ve been working on a lot of sprinting, tempo work and technique, so I think that all really helped. 

"I’m very happy with my race this morning."

Meyers triumphed ahead of fellow American Aspen Shelton, who clocked a time of 1:08.82.

Lawrence Sapp set an American record of 1:03.76 in the men’s 100m backstroke S14 preliminaries.

He went on to win the final in 1:03.88 with Garner Moss second in 1:10.99 and Jesse Greve third in 1:16.28 in another US podium sweep.

Results in Indianapolis will help determine the American team for the Lima 2019 Parapan American Games, which are scheduled to take place from August 23 to September 1.

Competition is due to continue tomorrow with the 50m breaststroke, 100m breaststroke, 400m freestyle, 50m freestyle, 4x50m 20 point freestyle relay and 4x100m freestyle relay S14 events.