The victory improved the U.S. record to 5-0 at the end of preliminary round play. The United States won Group B and will go against Angola, the fourth-place finisher in Group A, Sunday in a knockout game. Tunisia was 0-5 in the opening round.
The U.S. team, which had already wrapped up first place in Group B, coasted through much of the game and Coach Mike Krzyzewski used his starters on a limited basis.
The Tunisians played with more fire and were within two points late in the first half and trailed 39-33 at intermission. But the Americans pulled away in the second half with Gordon hitting four 3-point shots and a pair of U.S. spurts pushing the lead to 63-44 near the end of the third period.
Kevin Durant and Russell Westbrook each chipped in 14 points and Stephen Curry had 13 in the win.
Tunisia was led in scoring by Marouan Kechrid, who had 15 points, and Macram Ben Romdhane, who had 11.
The other three groups were won by Serbia, Turkey and Lithuania. Serbia captured Group A Thursday with an 84-82 win over previously unbeaten Argentina.
The round of 16 begins Saturday, with Serbia meeting Croatia and defending champion Spain taking on Greece. Turkey will play France and Slovenia will meet Australia Sunday. In addition to the United States-Angola game Monday, Russia will play New Zealand. Tuesday, it will be Lithuania vs. China and Argentina vs. Brazil.
Quarterfinal games will be played next Wednesday and Thursday. The semifinals will be held Saturday, Sept. 11 and the gold medal game will take place the following day.