Ruiz's 44th-minute header was enough to hand 'Los Ticos' a 1-0 victory over Italy -- ensuring their place in the last-16 of the World Cup for the first time since 1990. (Agencies)
"I cannot explain the emotions I am feeling right now," the Fulham forward said after the Group D match.
"We suffered so much in this game. We had dreamt of this moment, even though we knew people didn't believe us. We qualified ahead of teams much stronger than we are, so this is all a dream come true,” he added.
“We thank all those who did believe in us, as we've achieved something extraordinary considering our country is so small,” he said.
The victory at Arena Pernambuco came six days after Costa Rica shocked Uruguay 3-1 in their opening game.
With England already eliminated, Uruguay and Italy will now play for Group D's other second-round berth in Natal on Tuesday.
"We kept up our heads. It was a beautiful match," Costa Rica coach Jorge Luis Pinto said.
"The people of Costa Rica deserve this. They supported the team and me. This was for them,” he added.
Italy coach Cesare Prandelli said the stifling conditions had contributed to the Azzurri's flat performance but admitted Costa Rica were the better side.
"We knew this would be a particularly tough group. We will try to recover all our energy for the Uruguay game," Prandelli said.
"We didn't get our tactics wrong. They were very, very aggressive and we were trying to find different ways into the game but we didn't manage it,” he added.
Ruiz's 44th-minute header was enough to hand 'Los Ticos' a 1-0 victory over Italy -- ensuring their place in the last-16 of the World Cup for the first time since 1990.