Nwokocha ran a personal best of 22.47 seconds to finish third in heat 1 of the event to gain one of the automatic tickets to the semi-finals.
Cote d’Ivoire’s Marie-Josee Ta Lou won the heat with 22.30, while the Bahamas’ Shaunae Miller-Uibo was second with 22.40.
Nwokocha could have been joined by compatriot Blessing Okagbare but the latter was disqualified from the competition after failing a drug test.
She is one of Nigeria’s remaining hopes for a medal at the games.
Earlier on Monday, Team Nigeria’s Tobi Amusan had placed fourth in the women’s 100m hurdles final.