The victory left Team USA on top of the six-nation North American qualifying tournament with two matches remaining.
In the other regional qualifiers Wednesday, Mexico defeated Honduras 1-0 and El Salvador was a 1-0 winner over Costa Rica.
Mexico needed a penalty shot goal from Chauhtemoc Blanco in the 75th minute to avoid what would have been a costly tie with Honduras.
The United States leads the group with 16 points. Mexico has 15, followed by Honduras with 13, Costa Rica with 12, El Salvador with eight and Trinidad and Tobago with five.
The top three teams at the end of the 10-match, round-robin qualifying tournament will wrap up a spot among the 32 countries that will battle for the World Cup in South Africa beginning June 11, 2010.
The fourth-place team from the North American group will take on the fifth-place team from South America in a two-match playoff to determine another World Cup spot.
Trinidad and Tobago, which is now out of the running for a World Cup position, had several scoring chances in the first half against a shaky American defense.
The United States picked up the pace in the second half, however, and Clark came up with the goal by bending a 30-yard shot past goalkeeper Clayton Ince. Tim Howard preserved the shutout in goal for the United States.
The Americans will next be in action in Honduras Oct. 10 and then wrap up qualifying against Costa Rica Oct. 14 at a site to be determined in the United States. A win in either match would put the United States in the World Cup.