Herediano were held to a 2-2 draw at home to Deportivo Saprissa and Alajuelense capitalised, beating Belen Siglo XXI 3-1.
Jose Ortiz struck a brace for Oscar Ramirez's Alajuelense as they held on for an important victory in San Antonio de Belen.
He opened the scoring on 12 minutes before adding another shortly after the interval, only to see their lead reduced.
Anibal Arrieta pulled a goal back for the eighth-placed hosts before they fell two goals behind once more.
Camilo Aguirre struck for the visitors in the 68th minute to make it 3-1 and complete the scoring.
Herediano, who drew 0-0 with Cartagines last time out, came from behind twice to take a point against Deportivo Saprissa.
The first of the four goals came on 42 minutes through the league's top goalscorer Ariel Rodriguez, who tapped in the easiest of openers.
Leandrinho levelled on the hour-mark with a cracking 20-yard finish into the top corner from an angle, much to the delight of the home fans.
The visitors were awarded a penalty in the 82nd minute and a stuttering Carlos Saucedo made no mistake with the spot-kick.
Herediano responded once more as a counter-attack led to Leandrinho finishing in a one-on-one with three minutes remaining.
While Saprissa sit third, Herediano are a point behind league leaders Alajuelense.
Limon made it three straight league wins as Steven Calderon's brace led them to a 3-2 victory at home to Carmelita.
Santos de Guapiles thrashed Cartagines 3-0 in a match which featured two late red cards – one to each team.
Puntarenas hammered struggling Perez Zeledon 4-0 and Uruguay remain bottom of the table after a 2-1 loss at home to UCR.
