Zivkovic's contract with Partizan Belgrade, the club where the player dubbed the 'Serbian Messi' began his career in 2013, expired at the end of last season.
Capped five times, the 19-year-old midfielder is considered a rising star of the Serbia national team after helping his country to gold in the U20 World Cup last year.
Benitez, 23, arrives from Argentine first division outfit Lanus for an undisclosed fee.