LISBON, Portugal (AP) -- Joint Portuguese league leaders FC Porto and Benfica were both held to draws on Sunday.
Nine-man Benfica drew 2-2 at 10-man Nacional early, and Porto failed to take advantage of its fellow contender's slip as it was held 1-1 at home with Olhanense.
After Tiago Targino put Olhanense ahead in the seventh, Jackson Martinez equalized for Porto in the 55th before missing a penalty 10 minutes later.
Nacional went ahead in the sixth through Diego Barcelos, before Benfica leveled through Edson Mexer's own goal in the 15th. Jonathan Urretavizcaya then put Benfica ahead with a free kick in the 37th, only for Mateus Galiano to split the points in the 53rd.
Benfica's Oscar Cardozo and Nemanja Matic were shown red cards late, while Nacional's Marcal received his second booking.
The two front-runners remained unbeaten through 18 rounds, and are 15 points ahead of third-place Pacos Ferreira.
Also, Sporting Lisbon's struggles continued as it lost 1-0 at home to Maritimo.