Gracie Laney, Logan High senior runner, was sprinting to the finish line in the girls' 4x200m relay race.
The event, the Grizzly Invitational, was held on April 17.
Laney was confidently heading for victory, until Holly made a late entry to the race.
'I'd say probably about the 50-meters mark, I could feel something coming on me, and I thought it was a person. I thought it was the runner,' Laney told The Salt Lake Tribune.
'And then I kind of realized that it was really small.'
Video from the race shows Holly dashing from a grassy knoll above the track, dragging her lead behind her, and making impressive progress to catch Laney.
'After watching the video, I thought, 'Holy cow, that dog is so fast,' Laney said.
'So I thought it was kind of funny that I got beat by a dog.'
She said she was focused on finishing, but also concerned that the dog might bite her, or that she would step on the dog with her spikes.
The crowd's cheers rose to a crescendo - which Laney thought were for her, until she saw the dog.
Laney said she never found out who owned the dog, but she would like to meet her one day.
'Looking back, I really wish I had gotten a selfie or something with it,' Laney said.