The reigning European champions entered Saturday's match with Italy simply needing a result to guarantee their place in the semis with a game remaining.
A defeat would not have ended Portugal's chances of winning the group, though it would have come down to the final day against already-relegated Poland.
But that match is now dead rubber, as Portugal are set to contest the semi-finals in June 2019.
As a result, Portugal will now host June's inaugural UEFA Nations League Finals, pending a formal appointment by the UEFA Executive Committee at their meeting in Dublin on December 3.
Portugal were joined by Italy and Poland as nations looking to host and, with Saturday's result, with the requirement being two stadiums with a net seating capacity of at least 30,000.
The original bid proposed Porto's Estádio do Dragão and the Estádio D. Afonso Henriques in Guimaraes as host venues.
All of the other potential semi-finalists will come down to the final match day of the League A groups.
In Group 1, the Netherlands visit already-relegated Germany on Monday. Though the Dutch are in second place behind France, a win or draw would see them pass the World Cup champions and make the semi-finals.
In Group 2, Belgium and Switzerland will meet to decide the who finishes top. A result on the road Sunday is all the Red Devils need to make the semi-finals, though they will be without Romelu Lukaku for the contest.
Group 4 is the most wide open with all three teams capable of winning. Croatia and England meet at Wembley Stadium on Sunday knowing that the winner of the match will go to the semi-final while the loser will be relegated to League B. However, should the match finish a draw, Spain will be the team that makes their way through to the semi-finals.