The Americans, seeking their fifth straight Olympic title, had to overcome a narrow deficit in the second period and owned only a 4-point lead at halftime. Croatia was still within 7 heading into the fourth period.
A 28-9 outburst over the closing quarter, however, turned the game into a one-sided affair. It was the 34th consecutive Olympic victory for the United States.
Charles scored 14 points, Angel McCoughtry had 13 in her first Olympic appearance and Candace Parker had 11. Croatia was led by Jelena Ivezic with 22 points.
Croatia had a 23-21 advance during the second quarter, but Diana Taurasi put the Americans in front for good with back-to-back 3-pointers.
The United States is playing in Group A during the preliminary phase of the Olympics, during which the Americans will meet the other five members of the group. The top four at the end of round-robin play earn quarterfinal berths.
In other Group A action Saturday, China surprised the Czech Republic 66-57 and Turkey was a 72-50 winner over Angola. The United States will next play Monday against Angola.
The highlight game in Group B Saturday came when Russia fought off Canada 58-53.