Goals to Gaston Pereiro, Ivan Alonso and Sebastian Fernandez inspired visiting Nacional to victory in the round 11 fixture at the Estadio Centenario on Saturday.
Pereiro broke the deadlock in the opening minute, before the Uruguayan Primera Division's top goal-scorer Alonso (11 goals) and Fernandez completed the scoring in the final minute.
Nacional, who have won eight games on the bounce since losing to El Tanque Sisley in August, are seven points clear at the summit with four matches remaining after Racing drew at Rentistas.
Racing's Mauricio Affonso cancelled out Gustavo Alles' sixth-minute opener within two minutes in a 1-1 draw on Saturday.
River Plate jumped up to fourth in the standings after defeating Defensor Sporting 2-0.
In a match that saw both teams play the second half with 10 men, River came out on top courtesy of first-half strikes from Michael Santos and Cristian Techera.
River's win saw them climb above Defensor Sporting and El Tanque Sisley, who were beaten 1-0 by Sud America.
Third-placed Penarol are level on points with River but ahead on goal difference, despite crashing to a 3-2 defeat at home to Rampla Juniors.
In other results, Matias Perez and Rodrigo Viega were both on target as Juventud accounted for Atenas 2-1.
Cerro climbed off the bottom of the table with 2-1 triumph over fellow strugglers Wanderers, following Tacuarembo's goalless draw against Danubio.
