The Americans put on the defensive clamps during the second quarter, holding Angola to six points while building a 41-18 lead at the break.
The winning streak for the U.S. Olympic women's team reached 35 games and the Americans will next meet Turkey, which has been the surprise team of the tournament.
Turkey was one of the last teams to make it to the Olympics, doing so in a qualifying tournament played in its own country.
Like the United States, Turkey has won its first two games in Group A and will try to pull off a huge upset Wednesday.
Turkey defeated the Czech Republic Monday 61-57.
In Group B, France and Russia are unbeaten after two games. France defeated defending silver-medal winner Australia in overtime 74-70. Australia tied the score at the end of regulation with a 55-foot 3-point shot.
Russia was a 69-59 winner over Brazil.