The St Etienne midfielder's strike seven minutes into the second half of yesterday's Group H encounter proved enough for Ottmar Hitzfeld's side to beat the European champions - and left Fernandes stunned.
"I don't think I realise what is happening right now," said the 23-year-old. "I'm a bit surprised. It's a very special moment for our country and I'm very happy. We were definitely very good against Spain and we played very well as a team."
The Spaniards dominated possession but the Swiss made the most of their chance. Fernandes, who was born in Cape Verde, said fortune had been on his side when he fired past Spain goalkeeper Iker Casillas.
"I'm not used to scoring goals so it's a bit of a surprise," he said. "In the goal, I did have a bit of luck as the ball fell to my feet and I anticipated the goalkeeper. I think Spain played well and they didn't underestimate us. They are technically a very good side and we were very lucky."
The Swiss next take on Chile in Port Elizabeth on 21 June. "We are in a great position now," Fernandes said. "But we have to remain concentrated for our next game as Chile will be a difficult rival."