Striker Jorge Djaniny got the home team up and running with a 26th-minute opener and substitute Saleh Gomaa came on to give Manuel Machado's team breathing space by doubling the advantage midway through the second period.
The result leaves Nacional five points behind third-placed Porto, who host Pacos Ferreira – two points and a place behind third-bottom Belenenses - on Sunday, while fifth-placed Estoril are four points back ahead of their Monday night trip to Academica.
Elsewhere on Saturday, Vitoria Guimaraes lost 3-2 at 10-man Vitoria Setubal as an unlikely comeback bid fell just short.
The hosts took an early lead through Ricardo Horta and, during a nightmare 10-minute period for Guimaraes during the second half, Ramon Cardozo and Rafael Martins added goals two and three before Francois was sent off for collecting two booking in quick succession.
Nevertheless, the visitors rallied and strikes from Crivellaro and Nii Plange set up a grandstand finish.
On Sunday, all eyes will be on the top-of-the-table derby clash between Benfica and Sporting Lisbon.
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