With a two point lead over last year's champions Porto and their destiny in their own hands, Benfica quickly took control.
Haris Seferovic opened the scoring after 16 minutes. Joao Felix doubled the lead seven minutes later and Rafa Silva added a third before half time.
Seferovic added his second in the 56th minute. Mid-table Santa Clara, from the Azores, replied with a goal by Cesar three minutes later.
Porto beat Sporting 2-1.
At the final whistle in Lisbon, Benfica fans began to celebrate the title with a concert of air horns in the streets.