Watched by 55,000 fans inside the Stadium of Light, Alex Grimaldo opened the scoring in the first minute but it was another 20 minutes before Haris Seferovic scored the first of his two goals.
Swiss international Seferovic's second arrived in the 27th minute as Benfica went into the break with a 3-0 advantage.
The floodgates opened in the second half with Joao Felix, a Pizzi penalty, Ferro, Ruben Dias, Jonas with a brace and Rafa Silva all on the scoresheet.
According to the BBC, it was the biggest win in 54 years in the Portuguese championship after Benfica clobbered Seixal 11-3 in 1965.
Benfica have now scored 57 goals in 21 league games this season while Nacional, who already had the worst defensive record in the top flight, have conceded 45 goals.
Sunday's rout came just three weeks after French champions PSG put nine goals past Guingamp in Ligue 1.