On 1 July 2007, Guarente's transfer back to Atalanta was officially completed. The 2007–08 Serie A campaign was his debut season in the top flight of Italian football. Alongside Fernando Tissone, Guarente formed part of a formidable midfield for the club that season, making 27 league appearances. Following the 2008-09 Serie A season, which included 33 Serie A appearances for the player, Guarente was rewarded with a new and improved contract with the club. He signed a new 5-year contract with an increase in net income in the summer 2009. Atalanta were relegated the following summer, and he was sold to Sevilla of the Spanish La Liga on 17 June 2010.