Mohamed Bayo gave Guinea the lead before captain Francois Kamano was sent off just before half-time. Frank Magri equalised early in the second half, but a winning goal eluded Cameroon. The brave Guinean showing on day three followed a string of unexpected results on Sunday with Cape Verde defeating Ghana, Mozambique holding Egypt and Equatorial Guinea drawing with Nigeria.
Earlier on Monday, Lamine Camara scored twice as title-holders Senegal outplayed Gambia 3-0 with the losers also having a player sent off late in the first half. Cameroon did not include Manchester United goalkeeper Andre Onana in the matchday 23 after he arrived in the Ivorian capital just a few hours before the kick-off.
Onana delayed his arrival so that he could play for United in a 2-2 Premier League draw against Tottenham Hotspur at Old Trafford on Sunday. Coach Rigobert Song chose Fabrice Ondoa as his starting goalkeeper with two other shot-stoppers, Devis Epassy and Simon Ngapandouetnbu, on the bench.
Cameroon, seeking a sixth title and second in four editions, were also missing star forward and leading 2022 Cup of Nations scorer Vincent Aboubakar, who was ruled out by a thigh injury. Guinea suffered a huge pre-match blow when Serhou Guirassy, scorer of 17 goals for Stuttgart in the Bundesliga this season, was ruled out by a knee injury.