A 2-1 win at home to Miramar Misiones saw Fenix stay top, with River Plate alongside them on 17 points but a weaker goal difference.
Danubio are two points back after drawing at home to Defensor Sporting, Penarol a further point behind after a loss against Cerro and Wanderers were beaten by River Plate.
Martin Liguera and Anibal Hernandez were on the scoresheet for Juan Tejera's Fenix, who held on for victory against Miramar Misiones despite Cristian Colman's 76th-minute goal.
Miramar Misiones are bottom after seven straight league losses, with their slump coming after they had won their opening game of the campaign.
River Plate ensured they would stay in touch with a 1-0 win at home to Wanderers coming courtesy of Leandro Rodriguez's 65th-minute goal.
Danubio were held to a 1-1 draw at home to Defensor Sporting.
Matias Alonso put the visitors ahead before Jonathan Alvez equalised but there were no goals after the two in the opening 14 minutes.
Like Wanderers, Penarol were also beaten as Juan Delgado's goal on the hour-mark was enough for Cerro to win 1-0.
Juventud claimed a rare win and inflicted Nacional's fourth loss in five league games with a 1-0 victory.
Jaime Baez's 89th-minute effort saw Juventud, who are second bottom, up to seven points, while Nacional's poor form sees them in mid-table.
Rentistas sit sixth after extending their unbeaten league run to four games with a 1-1 draw at home to El Tanque Sisley.
Racing are unbeaten in five after a 3-1 win at home to Sud America, while Cerro Largo and Liverpool played out an entertaining 2-2 draw.
