Smart finished with 18 points in the first half as the Cowboys led 38-28 at the break.
Nash took over the scoring load for Oklahoma State in second half. He scored 17 second-half points. Forte added 3 3-pointers in the second half.
He had a dunk and two free throws to make it 42-28.
Nash added a layup with 14:25 left to give the Cowboys a 15-point lead at 48-33.
Smart had a layup with 6:25 remaining to cap a 14-5 run and give Oklahoma State a 65-55 lead.
"You gotta give Oklahoma State credit." N.C. State coach Mark Gottfried said. "I thought they played pretty well. That was as poor a performance as we have had in a long time. I'm not sure we did a lot of things well. We came out casual and, like in a prize fight, they took it to us.
"It's my job to make sure we are ready to play. Tonight, we weren't ready to play. It's disappointing. We were playing for the championship of this tournament and came out very casual to start the game. I didn't like that at all. We didn't seem to make shots. We struggled to make baskets."