Clark took an impressive 0.34 seconds off the mark she set at last year’s World Championships as she crossed the line in 55.99sec at the Joe Selleh Track.

"It was tiring but I went through it just like I practiced," said the 23-year-old, who is coached by her mother Rosalyn, a silver medallist for the United States in the 4x400m at the 1976 Montreal Olympics under her maiden name of Bryant.

"I crossed the finish without slowing up.

"Breaking the world record takes hard work - I hope to break more records by next year and 2020."

The Arizona Grand Prix doubled as the US Nationals this year and many of the top American Para-athletes were in action.

Reigning world champion Jarryd Wallace added to his victory over 100m on the opening day with a straightforward win in the 200m T64.

The 28-year-old clocked 22.11, finishing more than a second clear of his rivals.

Daniel Romanchuk, who set a world record of 1min 29.66sec in the 800m T54 on the opening day, added two more national titles in his category.

The 20-year-old, who now holds the world record in the 800m and 5,000m T54, clocked 46.70 in the 400m and 2:53.64 in the 1,500m.

Six-time Paralympic gold medallist Ray Martin earned his second win of the competition with a convincing victory in the men's 400m T52 in 57.51sec, although he had to make do with second place in the 1,500m T52 behind fellow countryman Nicholas McCoy, who clocked 3:41.81.

Brian Siemann, 28, rounded off a highly successful competition as he added to his hat-trick of wins 24 hours earlier with T53 wins in the 400m, where he ran 50.55, and 1,500m, where he recorded 3:24.76.

London 2017 double silver medallist Amanda McGrory was unbeaten on day two, winning both the 400m T54, in 54.61, and the 1,500m T54, in 4:11.78.

Chelsea McClammer won the women’s 400m T53 title in 56.57 while Kym Crosby, clocking 1min 01.09sec, added to her gold medal collection in the women’s 400m T13.

Deja Young won two world titles at London 2017 and the 22-year-old showed she’s still the one to beat in her class as she took the win in the 100m T46 with a new 2018 world lead time of 12.42.

Out in the field, three-time world champion Lex Gillette continued his winning ways in the men's long jump T11.

The 34-year-old has won the event since the first Grand Prix back in 2013, and this time 6.20m proved good enough to take gold.

Paralympic champion David Blair won the men's discus F44 with a best of 62.92m and three-time world champion Jeremy Campbell took gold in the F64 class with 62.51m.

There was success for overseas Para-athletes too - Trinidad and Tobago's Paralympic and world champion Akeem Stewart threw 59.30m in the men's discus F43 and also won the javelin F43 with 55.96m.

Australia's world silver medallist Guy Henly managed 47.78m to win the discus F37, Mexico's Gabriel Buenaventura took the top spot in the men's javelin F46 with 54.05m and Canada's Alister McQueen threw 51.46m to win the javelin F64.