After his loan with Once Caldas had finished, he returned to Colo-Colo in June 2008, despite Fernando Astengo not planning on featuring him in the team. Millar made his first start against Universidad de Chile in a Copa Gato match that ended in a 2–1 victory at Tierra de Campeones Stadium in Iquique. Despite several starts, he found it difficult to break into the first team, with Astengo preferring to use him as a substitute.. With the arrival of Marcelo Barticciotto as coach, he was given a more permanent position in the first team, providing consistently good performances as a result. On 8 November 2008, Millar scored his first goal in the Barticciotto era against Cobresal in a 1–1 home draw. In the Championship playoffs second leg final, Millar was proclaimed a champion for third time in his career, after he scored the goal of the championship in the 3–1 victory against Palestino, by eluding the goalkeeper Felipe Núñez and playing masterfully.