The Scot’s victory was an emphatic one, finishing more than half a second ahead of American Cassandra Tate in second.
“I’m absolutely delighted,” she said. “It wasn’t even a great race, the last hurdle was very poor so I think there’s a lot more to come. If I get it right, I can definitely go sub 54 seconds.”
Her compatriot Lynsey Sharp ran the second fastest time of her life as she clocked 1:57.75 to finish sixth in a electric 800m, South Africa’s Caster Semenya cementing her status as the hottest gold medal favourite on the athletics programme in Rio.
Semenya ran a PB, and the fastest time in the world since 2008, to win in 1:55.33.
Steph Twell, fresh from her 5,000m bronze at last week’s European Championships, wiped almost 10 seconds off her 3,000m PB to finish fifth in 8:40.98.
Mo Farah honed his finishing speed ahead of the Rio Olympics as he finished fifth in a high-quality 1500 metres field.