Muir, who took gold at an indoor competition in Hungary earlier this month, recorded her second consecutive win of the Olympic campaign with a total of 1,361 points.

The Briton, ranked 17th in the world, edged out Russian Uliana Batashova in the laser run with a time of 12min 09.23sec.

Batashova was forced to settle for the silver medal, while compatriot Gulnaz Gubaydullina did enough for bronze.

Gubaydullina, who won the world title at the same venue in the Egyptian capital back in 2017, amassed 1,349 points.

But the plaudits belonged to Muir, who overcame difficulties in the riding section of the race to clinch victory in the first race of the World Cup season.

"It hasn't sunk in yet, I can't quite believe it, to be honest," Muir said.

"I had a good fence and my swim was OK, but in the riding my stirrup snapped halfway round and I couldn't believe it - I thought 'the one day when I fence well and I am going to come off my horse'. 

"I was so relieved to get round.

"In the laser run there were lots of quick runners round about me and I tried to stick with them, and not kill myself too early. 

"It could have been anyone's race.

"I can't believe it - it feels amazing."

The event in Cairo continues with the men's final tomorrow.