Libertad clinched the Clausura championship to continue their recent dominance of Paraguayan football.
Colombian Vladimir Marin set them on their way by scoring from a free kick and a header in a four-minute spell midway through the first half.
Jorge Cacares headed one back for Sol in the 33rd minute, the refereeing ruling that the ball crossed the line before being cleared by goalkeeper Victor Centurion.
Victor Caceres and Manuel Maciel added further goals in the second half.
Libertad finished with 44 points from 22 games, one ahead of Guarani whose 2-0 win over 12 de Octubre was in vain, although it guaranteed them a place in next year's South American Libertadores Cup.
Cerro Porteno and Olimpia, traditionally the country's two big clubs, finished third and seventh respectively after another disappointing season.
Libertad previously won the 2006 and 2007 titles when only one championship was held per season. This year, the Paraguayan FA changed the system to two separate championships known as the Apertura and Clausura and Libertad won both.