Sporting Lisbon missed the chance to move top of the Primeira Liga table as visiting Academica held firm to claim a 0-0 draw on Sunday.
On a weekend that saw all three title contenders slip up, Sporting's draw at Estadio Jose Alvalade will have frustrated coach Leonardo Jardim, who saw his side dominate but fail to score.
Table-toppers Benfica could only manage a 1-1 draw at Gil Vicente on Saturday, while Porto, who sit two points behind Sporting in third, lost 1-0 at Maritimo.
Yet Sporting could not take the chance presented to them as they were continually frustrated by Academica goalkeeper Ricardo.
The hosts had 20 shots on goal to the seven of their opponents, with 10 on target, but failed to break the resistance of mid-table Academica.
In Sunday's other match, Belenenses pulled three points clear of the relegation zone with a 2-1 win over Braga.
After a goalless first half, Miguel Rosa fired Belenenses ahead in the 50th minute and they doubled their advantage just eight minutes later.
Filipe Ferreira was the scorer of the second, but Braga set up a tense finale through Alan's strike, his third in two matches, with 22 minutes left.
Belenenses were able to hold on, securing only their third league win this season.