Porto held by Pacos on opening weekend
Benfica were also held to a 1-1 draw at home to Maritimo as six of the opening weekend's seven games ended in stalemate.
Pacos opened the scoring with a Ricardo header in the 12th minute and Porto were in further trouble when Brazilian Hulk was sent off for a second yellow card in the 55th minute.
But the champions salvaged a point when Colombian striker Radamel Falcao Garcia scored with a 78th minute header on his league debut following his move from Argentina's River Plate.
Benfica also came from behind, Maritimo's Alonso converting a penalty after defender David Luiz handled in the 25th minute.
Paraguay striker Oscar Cardozo missed a 75th minute penalty for Benfica but substitute Weldon headed in from a Fabio Coentrao free kick ten minutes later.
Sporting, last season's runners-up, drew 1-1 away at Nacional Madeira on Saturday.
Braga were the only team to win at the weekend. They beat Academica 1-0 on Saturday.