The blistering run shaved more than a tenth of a second from the previous mark of 52.34s set by Russian Yuliya Pechonkina in 2003.

“I’m just shocked,” said the 29-year-old Muhammad, who suffered concussion after a fall during training two weeks ago.

“I’ve been kind of hitting that time in practice consistently and my coach was like, ‘There’s no way you can’t do it’.”

Teenager Sydney McLaughlin was second in 52.88s, just 0.13s shy of her personal best, with Spencer third in 53.11s, as all three runners made the US team for September’s world championships in Doha.

Noah Lyles also qualified after running 19.78s to win his 200m showdown with 100m champion Christian Coleman.

The two were side-by-side before Lyles pulled away in the last 60m.

Coleman claimed second (20.02s) with Ameer Webb third (20.45s).

The women’s race went to Dezerea Bryant in 22.47s.

Craig Engels edged Olympic champion Matthew Centrowitz in the men’s 1,500m by four-hundreths of a second, winning in 3:44.93s.

The men’s 110m hurdles was the reverse of the US collegiate final with Daniel Roberts winning over Grant Holloway in 13.23s. Holloway clocked 13.36s.

World indoor champion Sandi Morris cleared 4.85m to win the women’s pole vault, while world champion Emma Coburn won her sixth consecutive US 3,000m steeplechase title in 9:25.63s.

Lopez Lomong used a late surge to defeat Olympic 5,000m silver medallist Paul Chelimo in the men’s event and claim his second title of the meet after winning the 10,000.

Lomong will not be doubling up in the 5,000 and 10,000 at Doha, however, because he lacks the standard in the longer distance.