siːˈɛɹə mˌeɪd hɪz deɪbjˈuː ɪn pɹəfˈɛʃənəl sˈɑːkɚ wɪð jˌuːnɪˈɑːn ɛspɐnjˈoʊlə ˌɔn noʊvˈɛmbɚ nˈaɪntiːnhˈʌndɹɪd ˈeɪɾi ˈeɪt ɐɡˈɛnst ðə jˈuːnɪvɚsˌɪdæd də tʃˈɪli.
Sierra made his debut in professional soccer with Unión Española on November 1988 against the Universidad de Chile.