The leaders claimed a point from their trip to third-place UCR after a goalless stalemate, while Herediano stormed into the top four after a 3-2 triumph over second side Deportivo Saprissa.
Saprissa struck first at the Estadio Eladio Rosabal Cordero in Heredia, David Ramirez finding the back of the net in the 10th minute.
But their defence failed to hold up, as Herediano struck three times in a 10-minute period to blow the game wide open.
Yendrick Ruiz, Verny Scott and Esteban Ramirez had all scored by the 21st minute, although David Guzman did pull one back for Saprissa before the interval.
But they could not find an equaliser in the second half, Jeaustin Campos' men falling to their second loss in their past three.
Herediano have games in hand on all of their rivals, most importantly one on Alajuelense.
Perez Zeledon snapped a four-match winless run with a 2-1 victory over Puma Generalena.
Zeledon had lost matches against top-four sides Alajuelense, Herediano and Saprissa in that run, scoring in all of their defeats, but they finally turned goals into points on Sunday.
Fabrizio Ronchetti and Josue Mitchell goals cancelled out Marvin Chinchilla's opener for Generalena.
Santos de Guapiles won 2-0 away at Uruguay for their second straight success, leaving them five points off the top four.
Carmelita are above Santos on goal differential, and four points behind fifth-place Cartagines after beating their potential top-four rival 2-1.
Cartagines' loss was their third match without success, as Herediano leapt above them into fourth.
Belen Siglo XXI climbed into ninth, after a 1-0 victory over Limon.
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