The Charleroi of Belgium striker also provided the assist for the fourth goal scored by Okereke.
A strong Nigerian side was boosted by Francis Uzoho, Kelechi Nwakali, Samuel Chukwueze, Osimhen and Taiwo Awoniyi all in the starting line-up in the explosive encounter at the Stephen Keshi Stadium, Asaba.
With two goals deficit off the first leg played last Wednesday,Nigeria dominated the encounter initiating a flurry of attacking moves but poor marksmanship counted against them from getting the opening goal which they badly needed.
The first real chance of the game came the way of Awoniyi but the Royal Excel Mouscron striker sent his effort just over the crossbar after Libya goalkeeper closed him down.
Porto midfielder Kelechi Nwakali then came close to scoring in the 17th minute but saw his free-kick, which left the guests’ goalkeeper motionless, came off the upright. The follow up was skyrocketed by Porto’s Nwakali amidst claim of handball which the referee waved off.
The deadlock was eventually broken in the 31st minute through Osimhen as the Chaleroi striker prodded home after free-kick was spilled by Libya’s goalkeeper.
Osimhen, who is on loan from Wolfsburg, was unlucky not to pull the tie level in the 44th minute as he unleashed a thunderous shot which came off the upright before the Libyans scrambled it into safety.
Nigeria continued from where they left off when the second half resumed but they only created less chances as the game drifted towards its crucial stage.
Osimhen was to get the much-needed second goal in the 66th minute as Libyan goalie, who has been the standout player for his side with key saves, spilled a cross allowing the striker to jab into an empty net.
Osimhen completed his hat trick in the 82nd minute after he broke away from the central defenders courtesy of a through ball from Nwakali to put Nigeria ahead on aggregate.
Substitute Okereke proved to be an icing on the cake in the final minute of additional time as he finished off a well-crafted goal after Osimhen back-heeled a rebound for him to blast home under challenge from two Libyan defenders.
Meanwhile, the coach Imama Amakapabo said the drafting of four players from the Super Eagles helped solidify his side.
He lamented that they suffered a 2-0 defeat in the first leg because they didn’t know anything about their opponents prior to the tie.
“It was a great result for us; we suffered in the first leg because many of these guys were playing together for the first time and we didn’t have any information about Libya. I watched the video of the first match several times and I was able to get the strength and weaknesses of the Libyan team. I think that informational helped us today,” he said.