The Central Americans sprung arguably the biggest surprise of the tournament so far when they turned over Oscar Tabarez's side 3-1 to top Group D after one round of matches.
Edinson Cavani's penalty looked to have set the much-fancied Uruguayans on their way, but Joel Campbell sparked a comeback with a 54th-minute equaliser before Oscar Duarte headed Costa Rica in front.
Campbell then turned provider for Marcos Urena to seal the victory and with Italy to come in Recife on Friday, Tejeda is confident the Costa Ricans can continue to impress.
He told the Costa Rica Football Federation's official website: "Now we have laid down a marker of what we are capable of doing.
"Italy are going to become very attentive and we will give them everything, because they know that we are not an easy opponent.
"I normally sleep fine after matches, but I could hardly sleep, maybe I slept an hour.
"Mostly because it was a very intense game, played with much courage resulting in happiness. It is something that you live through every day."
Duarte echoed his colleague's sentiments, adding: "This is just the start and we have our feet on the ground.
"It was a very important win for us and for the whole country, but work continues and the hardest part is on its way."
