Mary King and Mellow Jazz and Abby Chisholm on Withypool Common during the ride.
And she completed at 12.8kph, fast enough to be listed among the possibles for a Gold award had she completed the second day at a similar speed with her horse clear of veterinary penalties.
King was riding Mellow Jazz, a 15hh Arabian gelding who in 2004 competed on a British team in France and is owned by Karen Jones from Culmstock, Devon. "He was wonderful out on the moor, very tough and so nimble," King said afterwards.
"I am always keen to try something new and having watched the endurance competitors at the World Championships last year I jumped at the chance to try it myself.
"The preparation was impressive. The owners and riders are so dedicated, and the vetting was an education.
"Riding with my stirrups so long was strange, but I think I was fit enough. I'll know tomorrow morning!"
And she added "I would love to come back and try it again - as long as I can ride Jazz, of course."
King was escorted over the Exmoor course by endurance Young Rider champion Abby Chisholm, 15, from Lydford on nearby Dartmoor.
"Riding with Mary was a dream come true," she said. "She is very competitive!"
Crossing one of the many streams on the trail.