A stunning show from the 28-year-old, barely 24 hours after she decided to opt out of running the distance in Tokyo in order to throw everything into her quest for gold over 1500m.
With Prince Albert and a cast of millionaires watching on, Muir clocked 1min 56.73sec to royally demolish Lynsey Sharp’s existing Scots best to become the second-quickest Brit of all-time.
“I know I am in great shape,” Muir said. “This is my last race before Tokyo, so I just wanted to give it my best and put on paper the sort of shape that I know I am in and I am just so happy with that.
“Running 1:56 is giving me huge confidence for Tokyo. I will only be running the 1500m now, I decided that only a couple of days ago, but yes, I couldn't have asked for a better performance ahead of Tokyo.”
Jemma Reekie, in second, was also inside Sharp’s old time with a new personal best of 1:56.96. The 23-year-old was heading the charge to the line before her training partner swept by.
For a few priceless strides, Muir was blocked behind her before plotting her escape. A clear run and the European champion could possibly have claimed yet another of Kelly Holmes’ British records.
But it bodes so well for Reekie who stared down several of her potential Olympic 800m rivals and saw them blink first.
“Having a training partner like Jemma is huge,” Muir added. “Jemma has made me a much faster 800m runner. We push each other so much and we've both run 1:56, so I have definitely become faster because of her.
“I am going to go home tomorrow, have a week at home before flying out to Tokyo and just train as hard as I can, so I am in even better shape in Tokyo. I want to win a medal, that is all I am focusing on.”
Timothy Cheriuyot won the men’s 1500m in a personal best of 3:28.28. Two weeks out from the Olympics, Kenya have yet to rule whether the world champion, who came fourth at their trials, will be promoted into their Tokyo team in a decision that will weigh heavily on the medal chances of Josh Kerr and Jake Wightman.