Brazil 1-0 USA
Adriano celebrates after scoring the winner
Adriano was Brazil's hero with the only goal in an unconvincing win in Lyon that got the world champions' Confederations Cup campaign back on track.
Brazil can now reach the semi-finals by beating Turkey in their final group game on Monday.
The defeat means the US are eliminated whatever their result against Cameroon.
Adriano scored after 22 minutes when American defender Gregg
Berhalter hesitated with the ball on the edge of his area.
US goalkeeper Tim Howard parried Adriano's first effort but the striker fired the rebound into the open net.
Howard, who has been strongly linked with a move to Manchester United, put in an impressive display as the US failed to pose an attacking threat.
But Brazil were themselves disappointing, failing to capitalise on so much possession.
Ronaldinho's 75th-minute free-kick was a rare highlight but, as so often, Howard was in the right place to prevent a second goal.
Brazil: Dida; Juan, Lucio, Belletti, Kleber; Ricardinho, Emerson (captain), Kleberson, Alex; Ronaldinho; Adriano
United States: Tim Howard; Gregg Berhalter, Steve Cherundolo, Carlos Bocanegra, Cory Gibbs; DaMarcus Beasley, Pablo Mastroeni, Earnie Stewart (captain), Chris Klein; Landon Donovan; Clint Mathis
Referee: Lucilio Cardoso Batista (Portugal).