Turning Point: Portugal trailed 23-16 late in the first quarter and were outscored 20-12 over the next eight minutes.
Game Hero: Spain's Pau Gasol had a game-high 20 points on eight of nine (89%) shooting.
Stats Don't Lie: Spain shot 33 of 67 (49%) from the floor while Portugal were 25 of 62 (40%).
Spain outrebounded Portugal 41-35.
Spain blew out Iberian neighbours Portugal 87-73 on Thursday for their second win in as many games at the EuroBasket in Panevezys.
Sergio Scariolo's men threatened to deliver a first-quarter knockout and led 26-16 after 10 minutes played.
Portugal tried to stay within striking distance but Pau Gasol killed off their hopes early on.
Gasol poured 10 of his game-high 20 points in the second quarter as Spain's lead ballooned to 53-36 at half-time.
Portugal were held to just eight points over the next five minutes and trailed 69-44 before Scariolo sat down his starters.
The defending champions again got a big contribution from Juan Carlos Navarro.
The Barcelona scoring machine finished with 17 points and five assists and also came up with three steals.
Antonio Tavares led Portugal with 17 points.
Portugal have now slumped to back-to-back defeats and will take Poland on Friday.