Cerro Porteno defeated 3 de Febrero 2-1 to move to six points after two rounds of the Division Profesional's Apertura season but Rubio Nu kept the pressure on the leaders with a crushing victory over their city rivals.
Rubio Nu have four points and are just ahead of third-placed Libertad on goal difference after the latter drew 0-0 with Sportivo Luqueno.
Jorge Ortega started Rubio Nu's rout of Nacional in the 19th minute, bursting onto a long ball before striking a half-volley from the edge of the area that clipped the post on its way into the net.
A 55th-minute penalty from Silvio Torales saw Nacional equalise but the visitors had no response to Rubio Nu's three second-half goals.
Francisco Gomez struck the home side's final goal, thrashing the ball into the net after Nacional's goalkeeper had blocked the midfielder's initial shot.
The victory continued Rubio Nu's recent dominance of Nacional - four games without a loss, including three wins.
After Oscar Romero had given Cerro Porteno a 1-0 lead at half-time, 3 de Febrero equalised just before the hour-mark when Juan Pablo Raponi expertly chipped the home side's goalkeeper Roberto Fernandez.
