Ablett was drafted by with their fifth selection, and was the fortieth overall draft pick in the 2001 AFL draft under the father–son rule. Ablett made his senior debut for the club in the opening round of the 2002 AFL season, where he gathered 8 disposals and took 4 marks. Ablett made twelve senior appearances in total during the season, before spending the latter half of the year with the reserves team. Playing as a small forward, he helped the club's reserves team win the 2002 VFL premiership against Port Melbourne. After achieving premiership success with the reserves team in the previous year, Ablett established his position in the senior side the following season. Ablett alternated as a small forward and midfielder, scoring 26 goals and appearing in all of Geelong's senior fixtures during the 2003 AFL season. In round 2 in a loss against North Melbourne he received his first Brownlow vote, in a performance in which he registered 22 disposals and a goal. Ablett finished the year ranked first at the club for tackles (77) and inside 50s (89), as well as second for hard-ball gets (65). Following another season without participation in the finals series, Ablett and his teammates began their 2004 campaign with an appearance in the pre-season competition final against . Geelong would qualify for its first finals series in four years, being eliminated in the preliminary final by the . Ablett made 21 appearances in total over the course of the season, and kicked a career-high 35 goals. He once again finished the year ranked first within the club for total tackles (93), and was awarded the club's Best Team and Most Constructive Player award at the end of the season.