Porto beat Rio Ave 2-1 away from home on Sunday to claim its sixth win in six matches in the Portuguese league this season.
Danilo Pereira broke through for Porto in the 54th minute before Moussa Marega scored what proved to be the winner in the 67th. Nuno Santos pulled one back for Rio Ave with 10 minutes left.
Rio Ave lost defender Marcao to a second yellow card in the 89th.
Benfica lost 2-1 at Boavista on Saturday, when Sporting Lisbon beat Tondela 2-0 to keep its perfect start.
The weekend left Porto and Sporting atop the league with 18 points. Maritimo is third with 15, while defending champion Benfica is fourth with 13.