Grand Final prompted then-Roosters coach Ricky Stuart to move Minichiello to . His move to fullback coincided with some of the Roosters' best football for the early part of the new millennium. It also saw him become an almost automatic selection for both NSW and Australia for the next few seasons. With the help of the recently New Zealand former Warriors fullback and newly appointed Roosters Premier League coach Ivan Cleary, Mini would become a vital part of the Roosters attack. His great performance in his new position soon paid off with selection for City in the 2003 City vs Country Origin match and for New South Wales in the 2003 State of Origin series, and went on to play in his 100th NRL game for the Roosters in the first Preliminary Final of the 2003 NRL Finals Series. He was declared Man of the Match in the Roosters 28–18 victory over the Bulldogs. The Roosters subsequently lost the 2003 NRL Grand Final to the Penrith Panthers, in which Minichiello played at fullback. Minichiello ran 4,571 metres with the ball in 2003, more than any other player in the competition. After that he was selected to go on the successful 2003 Kangaroo tour in which Australia defeated their oldest rivals Great Britain 3–0 to retain The Ashes. Mini played on the wing for the Kangaroos in all three tests due to the presence of Brisbane Broncos fullback Darren Lockyer, who was also the captain of the Kangaroos. In 2004, Minichiello was again selected to play for New South Wales but just five days out from Game I he was sacked for taking a mobile telephone out contrary to team instructions during a wild bonding session. However he fought his way back into the squad and help steered New South Wales to its second series victory. He was named the Dally M Fullback of the Year in the 2004 NRL season, where he scored a career best 18 tries for the season. He also won the Harry Sunderland Medal as the player's player of the year. Mini went on to play at fullback for the Roosters in their 16–13 loss to the Bulldogs in the 2004 NRL Grand Final. It was the Roosters third Grand Final loss in four games since 2000. Minichiello was selected in the Australian team to go and compete in the end of season 2004 Rugby League