Cameroon 1-2 Nigeria
By Osasu Obayiuwana
BBC Sport, Monastir
John Utaka ended Cameroon's hopes of a third successive African Cup of Nations title as his goal secured Nigeria a semi-final place.
Utaka latched on to Kanu's pass to run clear and slide a shot in off a post with 17 minutes left.
Cameroon had led through a goal on the break, Samuel Eto'o hitting his first goal of the tournament.
But Nigeria levelled on the stroke of half-time courtesy of a superb curling free-kick from Jay-Jay Okocha.
The comeback earned the Super Eagles the right to face hosts Tunisia in Rades on Wednesday.
With both teams showing mutual respect for each other, the opening minutes of this quarter-final produced defensive caution.
Things warmed up in the 22nd minute however, when Okocha connected with a pass from Osaze Odemwingie and took a 25-yard shot that forced Cameroon goalkeeper Idriss Kameni to parry.
Growing in confidence, the Super Eagles continued to make incursions into Cameroon's area.
Joseph Enakahire and Osaze Odemwingie celebrate
Attempting to take advantage of gaping holes in the middle of the Indomitable Lions' defence, Odemwingie tried to make a run from the left side of the Nigerian defence.
But the 23-year-old was pushed by a desperate Modeste Mbami, who received a yellow card from Moroccan referee Guezzaz Mohammed.
Overlapping right-back George Abbey also had his chance to put Nigeria in front, but his 39th-minute volley did little to trouble Kameni.
Just as it appeared the first half would end goalless, the tactically aware Cameroon took advantage of a lack of organisation in the Nigerian defence to launch a quick-counter attack.
On the receiving end of a pass from the rear, Samuel Eto'o Fils made a run past sluggish central defender Isaac Okoronkwo before rounding goalkeeper Vincent Enyeama and curling a left-foot shot into the bottom corner.
Eto'o's 42nd-minute goal, his first of the tournament, provoked a unique reaction from his team-mates, as they playfully beat his chest in celebration.
Stung into a reaction, Nigeria wasted little time in seeking an equaliser.
But it took a trademark effort from the mercurial Jay-Jay Okocha for the Eagles to get back on level terms in first-half stoppage-time.
Taking a free-kick on the edge of the penalty area, the midfielder swerved the ball to the left, leaving Kameni motionless as it sailed by.
Inspired by their comeback, the Super Eagles maintained their initiative in the second half, with captain Rigobert Song and his defensive colleagues struggling to contain Nigeria's attacking play.
Song appeared to foul a threatening Odemwingie in the 53rd minute, but the referee turned down appeals for a penalty.
Nigeria's consistent efforts for the winner finally paid off in the 73rd minute when Nwankwo Kanu lobbed the ball into space for an onrushing John Utaka, who slotted the ball under Kameni's arm for the second goal.
Cameroon manager Winfried Schaefer tried to alter the tone of the game by substituting Patrick Mboma for Pius Ndiefi in the 78th minute.
The ploy nearly paid dividends 10 minutes later, when the burly forward hit the target, but the sharp reflexes of Enyeama ensured that Nigeria earned a historic win over their arch-rivals.
Cameroon: 1-Idriss Carlos Kameni; 2-Jean-Joel Perrier Doumbe, 3-Bill Tchato (18-Mohamadou Idrissou 62), 4-Rigobert Song, 13-Lucien Mettomo; 5-Timothee Atouba, 7-Modeste Mbami, 8-Geremi Fotso Njitap, 19-Eric Djemba Djemba; 9-Samuel Eto'o, 10-Patrick Mboma (11-Pius Ndiefi 78)
Nigeria: 1-Vincent Enyeama; 2-Joseph Yobo, 5-Isaac Okoronkwo, 15-George Abbey, 16-Ifeanyi Udeze; 4-Nwankwo Kanu (6-Joseph Enakahire 90+5), 10-Jay-Jay Okocha, 11-Garba Lawal, 14-Seyi Olofinjana; 7-John Utaka, 20-Peter Odemwingie (13-Pius
Referee: Mohamed Guezzaz (Morocco).