 Nyorai mberi kweiyi ndima - Prieto akaberekerwa muSegovia, uye akaita kutanga kwake kwenyika dzose pa1983 European Athletics Junior Championships, achiisa yechishanu mu10,000 m kufamba. Akauya wechinomwe mumakwikwi emakiromita makumi maviri ekufamba pa1985 IAAF World Race Walking Cup ndokuzoenderera mberi kuhwina menduru yebronze muchiitiko ichi pa1986 European Athletics Championships. Akazvisimbisa somumwe wevatambi veSpain vanotungamirira, achikwikwidza paWorld Championships muAthletics muna 1987uye 1991. Prieto akakunda menduru yake yechipiri yepasi rose pa1989 Summer Universiade, kwaaive menduru yesirivheri mumakiromita makumi maviri ekufamba kumashure kweItari Walter Arena. Akauya wechi13 pa1990 European Athletics Championships uye akapedza nzvimbo imwe pasi peiyo pa1991 IAAF World Race Walking Cup. 