Paul Bravo scored the first goal for the United States in the 27th minute by squeezing the ball past the near post after the Saudi defender Mohsin Harthi had inadvertently deflected a cross from Gregg Berhalter.
The United States were reduced to 10 men in the second half after the Paraguayan referee, Ubaldo Aquino, sent off their midfielder Matt McKeon for a second yellow card.
But Saudi Arabia were unable to break down a disciplined American defence to create any opportunities for their goalscoring sensation Marzouk Al Otaibi, who is the tournament's joint top scorer with the Brazilian Ronaldinho on six goals.
Brazil were due to face the host nation in the tournament's final in the Aztec Stadium late last night.
An unmarked Brian McBride clinched victory for the United States in the 78th minute with his second goal of the tournament when he headed in a long cross from Eddie Lewis.
Playing their fifth game in 10 days, Saudi Arabia's roller-coaster tournament contained a final twist when Aquino at first awarded a first-half goal to Abdullah Bin Shehan before consulting with his linesman and then awarding a free-kick to the US for a handball by Bin Shehan who received a yellow card.
With a repeat of its third-place performance in the 1992 four-nation Confederations Cup, the squad brought together by the new American coach, Bruce Arena, completed a highly successful tournament. They achieved a surprise group victory over once-mighty Germany and a narrow defeat to the recently crowned Copa America champions Brazil.