Portugal almost found the opener in the first minute, when Benoit Assou-Ekotto played a pass back to Carlos Kameni, who was disarmed by Liedson but the ball went out for a goal kick.
The opening minutes were played at a fast place as Portugal looked determined to break down Cameroon. In the 13th minute, Cristiano Ronaldo had a great chance to break the deadlock when he raced down the middle after being put through by Deco, but as he entered the area, he found a bigger man in Nicolas N'Koulou, who disarmed him twice.
Ronaldo almost scored just four minutes later, when he sprinted into the box before drilling a well-placed shot, but Kameni stretched himself to make the save.
The Seleccao would find the back of the net in the 32nd minute, as Paulo Ferreira combined well with Simao Sabrosa down the right, and the winger sent in a low cross into the middle the box for a running Raul Meireles to volley home.
In the following minute, Cameroon would be reduced to ten men as Eto'o lost his mind and was shown two yellow cards in the space of seconds, first for protesting, and then for a nasty challenge on Duda.
Portugal had an excellent chance to extend their advantage in the 38th minute, when Ronaldo moved past a defender near the edge of the box after a total of six step overs, before cutting inside and sending a low drive which Kameni had to punch away.
The second period began with three substitutions made by Portugal as Liedson, Simao and Paulo Ferreira made way for Danny, Nani and Miguel. The Seleccao doubled their lead just two minutes into the second half courtesy of Meireles, who picked up the ball at the far post after a cross from Nani from the right and looked to cross back into the danger area but his effort deceived Kameni and flew into the top corner.
Cameroon tested Eduardo for the first time of the match in the 52nd minute, when Eric Choupo-Moting found himself with plenty of room before him and unleashed a powerful shot from outside the box which the Portuguese 'keeper punched away to safety.
Such a chance did not scare Portugal, who remained in control and almost made it 3-0 in the 65th minute. Danny flicked the ball to the far post, where Nani struck with a soft touch but Assou-Ekotto cleared it on the goal line.
The hosts looked closer to the goal, but it would be the African nation to score, on 69 minutes, through Pierre Webo, who had come on just minutes before and jumped between two Portugal defenders to head home an Assou-Ekoto cross.
Portugal woke up with the Cameroonian goal and once again extended their lead to two goals ten minutes before full-time. A fast counter-attack saw Ronaldo assist Nani with a low pass, and the Manchester United winger, with just Kameni to beat, sent the ball over the goalkeeper's head to make it 3-1.
It was a well-deserved win for the Seleccao after a bleak 0-0 draw with Cape Verde a week ago. Portugal will still face Mozambique on June 8th before their first World Cup encounter with the Ivory Coast a week later.
You can see the goals from the game here.
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