Nigeria beat holders Cameroon in AFCON thriller
China-based forward Ighalo bundled home a scrappy opener but Clarence Seedorf's Cameroon hit back through Stephane Bahoken and Clinton Njie with two quick-fire goals before half-time.
Nigeria drew level as Ighalo volleyed in his second just past the hour and he then turned provider as he played in Iwobi to steer home three minutes later and set up an unexpected quarter-final clash with South Africa, who stunned hosts and favourites Egypt 1-0 in Cairo.
"It was a good win and it was a difficult game. Even when they scored to make it 2-1 we still believed we could score and come back," said Ighalo, as coach Gernot Rohr praised the resilience of the Super Eagles.
"I think we dominated in the beginning and we scored a good goal. At the end of the first half there was a lack of concentration and Cameroon took advantage," Rohr said.
"But my young team always continues fighting and never gives up."
Seedorf was frustrated by Cameroon's slow start although he could not fault the effort of his players.
"I feel disappointment obviously and also some anger because I thought we were a little bit tense in a few moments, but I have to appreciate the players have done everything they could today," he said. "It was not enough."
Nigeria eliminated Cameroon in the first knockout round the last time they were reigning champions in 2004, and their bid to repeat history looked on when Ighalo nudged Nigeria ahead after 19 minutes.
Moments after Michael Ngadeu-Ngadjui powered a header over at the other end, Peter Etebo hooked a deep cross to the far post where it was driven back across goal by Omeruo and Ighalo stabbed home via a huge deflection that wrong-footed goalkeeper Andre Onana.
It was the first time Cameroon had conceded in Egypt, but after scoring just twice in the group stage the Indomitable Lions matched that output in three frenzied minutes before half-time.
Bahoken pulled Cameroon level on 41 minutes when he ghosted in behind Omeruo to connect with a terrific whipped cross from Bassogog, and Njie soon fired them in front after outpacing Ola Aina to a flick-on, holding his nerve and balance to slip beyond Daniel Akpeyi.
Njie nearly got the better of Akpeyi again early in the second half, the Nigeria 'keeper superbly clawing the ball out from just inside his post after the Marseille winger's cutback was deflected towards goal.
Rohr introduced Samuel Chukwueze with an hour gone but it was Ighalo, the top scorer in qualifying, who came to the rescue once more with a thumping finish after Ahmed Musa chested a cross into his path.
Ighalo joined Senegal star Sadio Mane on a tournament-leading three goals and he played a key role in Iwobi's decisive strike on 66 minutes, threading the ball through to the Arsenal winger to side-foot past Onana.
Ngadeu-Ngadjui toed wide at a corner but Cameroon struggled to truly threaten Nigeria in the closing stages with Ighalo denied a hat-trick late on as Onana plunged low to his right to knock away the forward's header.