Kwesi Appiah's side earned their first point of the competition in their 2-2 draw with Germany as Gyan netted his first goal of the tournament, which was almost enough to hand them the win before Miroslav Klose rescued Joachim Low's side the draw.
Gyan told reporters: "I was just waiting for my chance. I had a couple of chances in the first game, I was a bit nervous today. I just had to get my composure.
"As a striker, people expect me to score goals and that is what happened today. It was great work. Tactically, we were perfect today. They are good in possession, we know we don't need to waste our energy.
"We believe that after what happened today, we can beat Portugal."
Ghana take on Portugal on Thursday at the Estadio Nacional de Brasilia.