Neither side were able to produce quality in the final third of the pitch in the early stages of the match, which led to few opportunities to break the deadlock.
Both defences remained on top for the rest of the first half as the teams went into the break goalless and without a clear-cut opening on goal.
However, in the second half the visitors took the lead through their first opening at goal as Salvador Agra displayed predatory instincts to find the net.
Estoril pressed late in the match and managed to snatch a point when Bonatini fired a low effort towards the bottom corner that beat the outstretched hand of Rui Silva to earn his side a point.
The home side rise to 11th in the table with the point, while Nacional also move up into eighth place.