UCR missed the opportunity to extend their lead atop the Costa Rican Primera Division table after they lost on Wednesday.
With second-placed Cartagines losing to Santos de Guapiles, UCR had the chance to open a five-point buffer at the summit but it was not to be as Deportivo Saprissa won 3-1 in Torneo de Invierno action.
Olman Vargas broke the deadlock for UCR in the eighth minute at the Estadio Ricardo Saprissa Ayma, though that was as good as it got for the visitors.
Juan Bustos levelled proceedings in the 27th minute, before Saprissa added two goals after half-time.
Heiner Mora gave the hosts the lead seven minutes into the second half, and the points were secured with two minutes remaining after Vargas turned the ball into his own net.
Despite the defeat, UCR remain top with 19 points from eight matches, two clear of Cartagines.
Saprissa ended a two-game winless streak to climb up to fifth in the standings.
Earlier on Wednesday, Santos de Guapiles closed the gap on UCR after fighting back to beat Cartagines 2-1.
Kevin Fajardo cancelled out Andres Lezcano's first-half opener at the Estadio Ebal Rodriguez Aguilar.
And Ismael Fuentes completed the comeback with a 90th-minute winner.
Santos de Guapiles, who have played two extra games than UCR, are within five points of top spot.
Wednesday's two other fixtures ended all square, with Puma Generalena drawing 1-1 at home to Carmelita and Belen Siglo XXI playing out a goalless stalemate against Perez Zeledon.
Meanwhile, Alajuelense and Herediano were not in action due to their CONCACAF Champions League commitments.
Alajuelense were scheduled to travel to Limon on Tuesday, while basement side Herediano were set to play Uruguay on the same day.