Fenix were beaten 2-1 at home to Rentistas and saw their lead cut to a point after Nacional came from behind to beat El Tanque Sisley 3-1.
At Nacional's Estadio Gran Parque Central in Montevideo, the visitors took a shock eighth-minute lead through Junior Arias.
But Gerardo Pelusso's men responded in the 24th minute when Juan Cruz Mascia struck and just after half-time they took the lead.
Henry Gimenez put Nacional ahead and substitute Andres Scotti sealed the points in the 71st minute.
Rentistas climbed up to eighth with just their third win of the season as they handed the league leaders their first loss.
Guillermo Maidana and Bruno Pinatares scored for the visitors and they held on despite Gonzalo Vega pulling a goal back for Fenix on 89 minutes.
Defensor Sporting grabbed the biggest win of the round, climbing to third after a 5-1 thrashing of Cerro Largo.
Giorgian De Arrascaeta scored a first-half brace before goals after the interval from Leonardo Pais, Felipe Conceicao and a Matias Alonso penalty.
Leonardo Rivero netted a consolation goal for the hosts in the 90th minute.
Elsewhere, Penarol came from behind to edge Wanderers 2-1, Danubio were 3-2 winners at Juventud and River Plate scored late twice to beat Miramar Misiones 2-0.
Mid-table sides Liverpool and Racing played out a 2-2 draw and Cerro remain the league's only winless side after a 1-1 draw at home to Sud America.
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