The Pythagoreans gained promotion to the Italian top-flight last season and needed to a win at the Stadio San Paolo to maintain their top division status.
But goals from Arkadiusz Milik and Jose Callejon - all thanks to the ever crafty Lorenzo Insigne who provided the assists for both goals - relegated the visitors.
Nwankwo, recently named in Nigeria’s 30-man provisional list for the World Cup, was on from start to finish but could not add to his seven-goal tally. Instead, it was Marco Tumminello that grabbed a last-gasp consolation for Walter Zenga’s side.
The 26-year-old ends what has been a breakout season on the very low as Crotone finished the 2017-18 campaign third-from-bottom.
The lanky forward played in 23 league games.