Having led 2-0 and 4-1, Nacional held on for a 4-3 victory over Fortaleza, who dropped to the bottom of the table thanks to the loss, despite conceding twice in the final 10 minutes.
George Saunders and Argemiro Vacca struck late for Fortaleza but it was not enough for the visitors, who remain winless in their past three matches.
Nacional's win took them three points clear of Millonarios (30 points) at the top of the Primera A standings after the latter suffered a shock loss on Saturday at lowly Uniautonoma, who leapfrogged Fortaleza.
In Medellin on Sunday, Nacional opened the scoring just after the quarter-hour mark in front of their home fans when Edwin Cardona's free-kick found the back of the net after bouncing in front of Fortaleza goalkeeper Andres Mosquera.
The match exploded in the final half hour with Jorge Ramos putting Fortaleza on the scoreboard with a nice finish from Vacca's through ball in the 65th minute before Nacional struck twice in quick succession.
Luis Paez struck in the 73rd minute for the league leaders, following good lead-up work by Jairo Palomino, while Cardona set up Nacional's fourth goal, which was scored by Fernando Uribe five minutes later.
On Saturday in Barranquilla, Uniautonoma forward Cristian Fernandes Mejia struck in the 50th minute to stun visiting Millonarios and end his team's five-game losing streak.
