The Americans had already clinched a berth in the final round of qualifying, but the win allowed Team USA to complete an unbeaten six-game schedule in Group 1 of the preliminary round.
The top two teams in each of the three groups advanced to the final round, which will be played over the course of 2009. Trinidad and Tobago, Honduras, Mexico, Costa Rica and El Salvador will join the United States in the final round-robin portion of qualifying in the CONCACAF region.
At least three of the six remaining teams will earn a berth in the 2010 World Cup, to be played in South Africa. The fourth-place finisher will have a chance to reach the World Cup in a playoff with the fifth-place finisher in South American qualifying.
Kenny Cooper opened the scoring in the 54th minute Wednesday and Adu tallied on a free kick 15 minutes later.
Elsewhere on the final evening of preliminary qualifying, Honduras downed Mexico 1-0 to win Group 2. Mexico lost two of its six matches and wound up tied for second place with Jamaica. The traditionally powerful Mexicans came uncomfortably close to being eliminated, but advanced based on a better goal differential than the Jamaicans.
The schedule for the final round will be announced Saturday. The games will be played in February.