Porto retained their place at the Primeira Liga summit following a 0-0 draw with second-place Sporting CP at Estadio Jose Alvalade.
Sergio Conceicao's side had the better of the chances in Lisbon - Moussa Marega heading against the crossbar in the first half - but were unable to come away with a win that would have extended their lead at the top to five points.
Porto were the main protagonists in the first half and, after Miguel Layun and Yacine Brahimi were denied by Rui Patricio, the Sporting goalkeeper rushed off his line and brilliantly took the ball off the toe of Vincent Aboubakar in a one-on-one situation.
Jorge Jesus' men did not threaten until the 43rd minute when William Carvalho diverted Bruno Fernandes' cross towards goal with a header that Iker Casillas was able to tip behind relatively comfortably.
Porto hit back in a frantic end to the first half, with Marega heading Ivan Marcano's delivery against the crossbar and Aboubakar nodding a follow-up effort straight at Patricio.
A tearful Adrien Silva was presented with a Sporting shirt commemorating his 241 appearances for the club at half-time, the midfielder having left for Leicester City in the transfer window.
Sporting showed greater urgency after the break but Fernandes rifled over after picking Danilo Pereira's pocket just before the hour mark.
Patricio made two further important interventions, keeping Marega out with 11 minutes remaining and saving Layun's stoppage-time free-kick, though reigning champions Benfica have a chance to move one point behind Sporting with a win at Maritimo later on Sunday.