Captain Chancel Mbemba was the Congolese hero in the second semifinal, scoring in the first minute of added time to beat eight-time World Cup qualifiers Cameroon 1-0 in torrential rain in Rabat.
Nigeria will face DRC on Sunday in the Moroccan capital, and the winners qualify for a six-nation FIFA inter-continental tournament in March. The African playoffs involved the best four group runners-up.
Bolivia and New Caledonia have already secured slots in the playoffs; Iraq or the United Arab Emirates will represent Asia; and there will be two qualifiers from the Central America/Caribbean region. Europe are excluded.
After semifinals among the four lowest-ranked teams, the winners of the two finals will secure places at the World Cup in the United States, Canada and Mexico.
Nigeria are seeking a seventh appearance at the global showpiece and DRC a second, having played in the 1974 tournament when the central African country was called Zaire.
Osimhen squandered a great chance to give Nigeria victory at the end of added time, firing wide with only goalkeeper Loyce Mbaba to beat.
But the 2023 African Player of the Year atoned on 102 minutes, firing across Mbaba into the far corner after being set up by Benjamin Fredrick.
He struck again on 110 minutes, controlling a long pass before once again beating the goalkeeper with a shot into the far corner.
After conceding an 89th-minute equaliser in regular time, Nigeria regained the lead when substitute Chidera Ejuke scored his first goal for the Super Eagles after 97 minutes.
Osimhen’s impact
Akor Adams had put Nigeria ahead on 78 minutes, and Mario Lemina levelled after 89 minutes.
Nigeria had a purple patch midway through the opening half with Osimhen coming close three times to breaking the deadlock.
The 26-year-old Galatasaray striker headed wide twice, then had an appeal for handball turned down after a VAR review.
There was another VAR check on the hour after Nigeria full-back Bright Osayi-Samuel pulled the shirt of Aaron Appindangoye in the box, denying the defender a chance to connect with a free-kick.
After a lengthy review, Gabonese appeals for a penalty were turned down by the South African referee.
The deadlock in a tense showdown was finally broken when Adams intercepted a misplaced Gabon pass, rounded Mbaba and scored.
There was an element of luck about the Gabon equaliser as goalkeeper Stanley Nwabali appeared to have the shot from Lemina covered until it took a deflection and sneaked into the corner of the net.
Akor Adams had put Nigeria ahead on 78 minutes, and Mario Lemina levelled after 89 minutes.
Nigeria had a purple patch midway through the opening half with Osimhen coming close three times to breaking the deadlock.
The 26-year-old Galatasaray striker headed wide twice, then had an appeal for handball turned down after a VAR review.
There was another VAR check on the hour after Nigeria full-back Bright Osayi-Samuel pulled the shirt of Aaron Appindangoye in the box, denying the defender a chance to connect with a free-kick.
After a lengthy review, Gabonese appeals for a penalty were turned down by the South African referee.
The deadlock in a tense showdown was finally broken when Adams intercepted a misplaced Gabon pass, rounded Mbaba and scored.
There was an element of luck about the Gabon equaliser as goalkeeper Stanley Nwabali appeared to have the shot from Lemina covered until it took a deflection and sneaked into the corner of the net.
DRC deny Cameroon
With just six world ranking places separating Cameroon and DRC, a close encounter was expected, and so it proved with few clear-cut scoring chances in a cagey clash before Mbemba struck.
Manchester United striker Bryan Mbeumo had the best opportunity for Cameroon midway through the second half, but his low shot was just off target.
A little earlier, Congolese veteran Cedric Bakambu was foiled by goalkeeper Andre Onana, who pushed away his shot at the expense of a corner.
Group winners Algeria, Cape Verde, Egypt, Ghana, Ivory Coast, Morocco, Senegal, South Africa and Tunisia secured the nine automatic qualifying places reserved for Africa.
With just six world ranking places separating Cameroon and DRC, a close encounter was expected, and so it proved with few clear-cut scoring chances in a cagey clash before Mbemba struck.
Manchester United striker Bryan Mbeumo had the best opportunity for Cameroon midway through the second half, but his low shot was just off target.
A little earlier, Congolese veteran Cedric Bakambu was foiled by goalkeeper Andre Onana, who pushed away his shot at the expense of a corner.
Group winners Algeria, Cape Verde, Egypt, Ghana, Ivory Coast, Morocco, Senegal, South Africa and Tunisia secured the nine automatic qualifying places reserved for Africa.
