Really great? There have not been that many really great in the world. Eh, depends on one's definition...
Probably the best Italian male player in the Open Era was Adriano Panatta.
He is the only man to ever defeat the great Clay/Grass King Bjorn Borg
at Roland Garros and he did it twice to prove it was no fluke, and went on to win Roland Garros in 1976
. He also helped Italy win their only Davis Cup title in history in the same year.
His highest ranking was #4 in 1976 and all in all he won 9 titles, 1 major, a finalist in 16 others.
He was at least very good.