Nigeria confirmed their place as group winners following a dominant victory over Sao Tome and Principe.
Osimhen hits three as Nigeria blew away Sao Tome and Principe 6-0 to confirm their place as the group winners.
The Super Eagles have already booked their place in next year's AFCON but still had group placement to play for in the final game of qualifying against Os Verde-Amarelos.
Playing at home in a packed Nest of Champions in Uyo, the Jose Peseiro-led side refused to be complacent against a team they put 10 goals past in the first-leg, inflicting more punishment on the visitor's goal difference.
How it happened
The Super Eagles were expected to steamroll a Sao Tome side on the wrong end of a 10-0 scoreline in the first-leg, and they lived up to expectations.
Osimhen scored four in the first-leg against this opposition, and in only 13 minutes, he scored the opener for this encounter, heading in an Ademola Lookman cross from a corner kick.
The Atalanta forward went from provider to score on the 27th-minute mark, cutting inside on his right foot before burying the ball in the goalkeeper's near post.
Taiwo Awoniyi, who started up front with Osimhen, made it three in the 51st minute, getting his goal after struggling to make an impact in the first-half.
Napoli's ace, Osimhen, was fouled in the box by the Sao Tome goalkeeper, and he made no mistake from the resulting spot-kick, taking his personal tally in qualifiers to nine, and Nigeria's in the game to four.
The inevitable striker completed his hat-trick in the 79th minute after he was played through by substitute Samuel Chukwueze.
The AC Milan man made it six soon after, combining with fellow substitute Victor Boniface as Nigeria grabbed another famous victory against the Central African team.