D'Alessandro pipped his fellow Argentine Juan Sebastian Veron, who finished second after winning the award in each of the last two seasons with Estudiantes, with 18-year-old Brazilian striker Neymar of Santos in third.
Oscar Tabarez was named the best coach in the annual poll conducted by the Uruguayan newspaper El Pais and recognised by the South American Football Confederation (CSF).
Tabarez led Uruguay to the semi-finals at this year's World Cup in South Africa and finished ahead of Marcelo Bielsa, who took Chile to the second round, and Estudiantes coach Alejandro Sabella, whose side won the Argentine Apertura title
Previous winners include Brazil's Romario and Cafu and Colombia's Carlos Valderrama.
D'Alessandro, with a fierce left-foot shot, incisive passing and volatile temper, has resurrected his career after joining Internacional in 2008.
He joined the growing number of Argentines in Brazil when he went to Porto Alegre-based Internacional in 2008 and helped them win the Libertadores - South America's equivalent of the UEFA Champions League - this year.
