The Americans prevented Emirates Team New Zealand from capturing the top prize in sailing in the first of the day's two scheduled races.
The second race in San Francisco Bay, however, was postponed due high winds -- something that has become commonplace in the series. Two races were scheduled for Friday.
It was the fourth win for the United States in the competition, but the Americans have been credited with only two victories because of a 2-point penalty assessed in a cheating scandal involving the team.
With an 8-2 lead, New Zealand needs to win only one more race in the best-of-17 showdown to capture the America's Cup.