Porto retained the lead on goal difference despite slipping to their first defeat of the season, 2-1 at Braga.
Porto and Sporting have 12 points from five games with Naval, who beat Beira Mar 2-1 at home on Friday, in third place.
Braga opened the scoring after 24 minutes through Brazilian striker Marcel, who connected with a neat cross from the left by his compatriot Wender.
Porto, without injured Slovakian defender Marek Cech and Brazilian striker Adriano, equalised three minutes before halftime through a header by striker Helder Postiga from a left-wing cross by winger Ricardo Quaresma.
Braga, the only Portuguese team to qualify for the UEFA Cup's group phase, went ahead again when defender Luis Filipe scored with a surprise shot after 56 minutes.
Sporting overcame 10-man Uniao Leiria 2-0 on a rainy evening in Lisbon. Winger Nani put Sporting in front after 34 minutes, tapping in a cross from the right by Brazilian striker Alecsandro.
Brazilian striker Liedson sealed the three points from a penalty, his first goal of the season.
Seventh-placed Leiria were reduced to 10 men after 73 minutes when defender Eder received his second yellow card for a foul on Nani.
Benfica grabbed their second win this season when they crushed promoted Desportivo Aves 4-1 at home on Sunday.
Benfica have seven points and one game in hand.
