Brenes, who entered in the match in 80th minute, sent in a low shot from inside the box that beat Miguel Montes to the far post as Costa Rica remained unbeaten in Group A after a 5-0 win over Cuba on Sunday.
Rodolfo Zelaya scored from a free kick in the 45th minute for El Salvador, which had withstood Costa Rica’s second-half surge until the closing seconds. El Salvador lost 5-0 to Mexico in its tournament opener.
“We are improving. I think we played 50 or 60 percent better than we played against Cuba,” Costa Rica coach Ruben Israel said. “We handled the ball al lot. We were able to shoot the ball a lot of times. But when you are not scoring, you’re not scoring.”El Salvador coach Ricardo La Volpe was angered by American referee Jair Marrufo’s decision to award four minutes of added time, then some additional time that allowed for Costa Rica to draw.