Lisbon, Dec 22 (IANS): Sporting were held to a goalless draw by Nacional and failed to increase their provisional lead in the Portuguese football league.

Sporting, who were hoping to clinch a sixth consecutive victory in Alvalade Stadium here Saturday, were under considerable pressure after Porto and Benfica's victories Friday and created poor scoring chances, reports Xinhua.

Algerian forward Islam Slimani scored in the 64th minute but fans were left bemused when his goal was disallowed by referee Manuel Mota for an alleged foul on Venezuelan striker Mario Rondon.

Nacional showed good defensive work and created a real threat through Brazilian striker Diego Barcellos, whose effort in the 57th minute went wide.

Nacional won the last round against Pacos de Ferreira after four consecutive draws and are now sixth in the Portuguese league with 21 points while Sporting are provisionally at the top and on even points with its rivals Porto and Benfica.

Sporting were without Cisse due to injury and Nacional without Edgar Abreu and Skolnik.