Ivory Coast cruised into the semi-finals, outclassing a young Guinea side who were not entirely disgraced.
Keita's opening goal came from a tight angle
Kader Keita put the Elephants ahead in the first half, shooting from an acute angle after a run down the right.
The other four goals came in the last 20 minutes as a fine Didier Drogba finish made it 2-0, then Salomon Kalou rounded the keeper to extend the lead.
Kalou bagged his second from six yards out, and Bakary Kone's 20-yard thunderbolt completed the rout.
Missing suspended captain Pascal Feindouno and injured defender Bobo Balde, Guinea were always likely to struggle.
Coach Robert Nouzaret used two 19-year-old midfielders, Mohamed Sakho and Mamadou Bah, against the might of Ivory Coast.
The game began at a very sedate pace, in hot and sticky conditions.
Guinea had a shot on target in the 23rd minute, Bah's effort from 25 yards going into the arms of Boubacar Barry.
But Ivory Coast then took control of the game, and two minutes later Keita put Ivory Coast ahead, shooting from a tight angle from the side of the box.
Guinea goalkeeper Kemoko Camara had left his near post uncovered, and should have done better.
Camara made an outstanding double save on 43 minutes, blocking a shot from Aruna Dindane then stretching to get to the ball that had rebounded to Salomon Kalou.
In first-half stoppage time a Didier Drogba shot from the edge of the area was heading into the top-right corner, but Camara made a fine save.
The Elephants continued to dictate the pace, but Guinea's Daouda Jabi almost levelled on 62 minutes, with a 20-yard free-kick that went inches wide.
Six minutes later Dindane failed to put the ball into an empty net, having rounded the goalkeeper.
But soon after, Drogba calmed the nerves of the Ivorians.
Exchanging passes with Arthur Boka, Drogba charged goalwards, collected inside the box and netted with a perfect finish.
Two minutes later, it was Kalou's turn to round the goalkeeper, walking the ball into the net, having received a Drogba pass.
Kalou's second, in the 81st minute, was the result of a three-man move that tore through the Guinea defence, as Bakary Kone passed to Yaya Toure, his cross finding Kalou.
Substitute Kone made it 5-0 with a screamer from just outside the area, flying into the top corner.
The Elephants have not been fully tested in their four victories so far, and remain favourites to lift the trophy on 10 February.
Ivory Coast: Barry, Boka, Meite, Eboue, Zokora, Toure Yaya, Romaric, Kalou, Drogba (Bakary Kone 76), Dindane (Arouna Kone 72), Keita (Fae 75).
Subs Not Used: Tiassa Kone, Loboue, Djakpa, Gohouri, Toure, Zoro, Tiene, Gervinho, Sanogo.
Goals: Keita 25, Drogba 70, Kalou 73, 81, Bakary Kone 86.
Guinea: Kemoko Camara, Ibrahima Sory Camara, Zayatte (Kalabane 83), Jabi, Diallo, Mansare, Bangoura, Bah, Sacko, Johnson (Soumah 61), Youla (Karamoko Cisse 60).
Subs Not Used: Diarso, Yattara, Bobo Balde, Habib Jean Balde, Alseni Camara, Mohammed Cisse, Correa, Sylla, Feindouno.
Booked: Zayatte, Ibrahima Sory Camara.