Born in Antofagasta, Toselli joined Universidad Católica youth ranks in 2001, being promoted to first-team by the coach Jorge Pellicer in 2006 for the Torneo Apertura, due to the departure of second-choice keeper Rainer Wirth to Deportes Temuco. The following year, after a notable performance in the FIFA U-20 World Cup, he made his club debut on 25 November, during a 3–0 home win to Coquimbo Unido played at San Carlos. The next season, he was challenging the goal with record-man José María Buljubasich, becoming the first-choice keeper, after their mistakes and its departure to Olimpia.