He would feature more frequently in 2001, under new manager Oscar Garré, making 10 appearances, netting the first professional goal of his career by opening the scoring for Huachipato in a 4–2 away defeat against eventual champions Santiago Wanderers, and scoring for the second and last time that season, netting the equalizing goal in a 2–2 home draw against Coquimbo Unido.

Mancilla would become a starter for Huachipato in the 2002 Clausura, playing 14 games, but would not manage to score again during the year, in a season that ended with a playoff quarterfinal away goals exit (3-3) to Universidad de Chile.

Mancilla would score in Huachipato's first leg 2–1 home victory, but they would lose 0–2 away to eventual champions Cobreloa in a 2-3 golden goal aggregate loss.

In the 2003 Clausura, Mancilla remained in the starting eleven, playing 16 matches and scoring 11 goals, in Huachipato's fourth consecutive playoff season, going scoreless in both of legs of a 3-5 quarterfinal exit to Unión Española.

In 2007, Mancilla moved abroad for the first time in his career, as he was sold to CD Veracruz of Mexico for $800,000, where he would remain for two seasons, scoring 15 goals in 39 appearances.

On 16 June 2008, Mancilla was transferred for an undisclosed price to Toluca where he would remain for four seasons, winning the 2008 Apertura, as the top goal scorer in the league, and the 2010 Bicentenario.

After his contract with Morelia expired in 2016, Mancilla played in 2017 for Lobos BUAP, scoring once in his final stint in Mexican football.

Mancilla finished his career by returning to his boyhood club Malleco Unido in the Segunda División Profesional de Chile in 2018, to honour his mother's wishes,[3] retiring from football at the age of 38.

Mancila would make 5 friendly match appearances during 2009 and 2010, but would not be considered for Chile's 2010 FIFA World Cup squad, leading to his international retirement in 2010.