Nwankwo notched his fourth consecutive effort in the Italian top-flight as Crotone moved to the 14th spot in the table with 34 points from 35 games.
Marcello Trotta gave the hosts a perfect start with his opener in the third minute before the Nigerian forward doubled the lead 12 minutes later.
Trotta extended the Pythagoreans’ lead with his second effort of the encounter in the 31st minute before Domenico Berardi reduced the deficit for Sassuolo just before half-time.
After the break, Nwankwo wrapped up his team’s victory at the Stadio Ezio Scida in the 89th minute.
The 25-year-old forward has now scored six goals in 20 league matches this term. He will be hoping to maintain his decent form in front of goal when the Pythagoreans visit Chievo on May 6.