Primeira Liga Wrap: Porto held by Nacional
It was a second successive draw for the leaders, who are unbeaten so far this season with seven wins and three draws from their 10 league matches.
Jackson Martinez had given Porto the lead in the 52nd minute on Saturday, but they were denied all three points when Mario Rondon struck with eight minutes remaining.
That result earned Paulo Fonseca's side a one-point lead at the top of the table, with Benfica in second following their 1-0 home win over Sporting Braga.
Nemanja Matic scored the only goal of the game in the 72nd minute to hand the hosts their fourth successive league victory while for their opponents, it was a fifth straight league defeat, an alarming slump in form after the four consecutive wins at the start of the season.