one, two, three, Go! this is how we would start a running race, or other games or competitions in the UK, so that everyone starts together. What is the Spanish equivalent?
It is going to be difficult to find a "source" for this... But what I am used to is
- Preparados... Listos... ¡Ya!
as a translation for "Ready... Set... Go!" (see for example a newspaper article titled like that), or
- Tres... Dos... Uno... ¡Ya!
- Uno... Dos... Tres... ¡Ya!
as a translation for "three, two, one, go!" or "one, two, three, go!" respectively. There even seems to be a Spanish learning book titled "Uno, dos, tres, ¡ya!".