The Americans were always going to be up against after midfielder Shannon Boxx was sent off in first-half injury time for a contentious second yellow card.
The Americans play Norway in Sunday's third-place game.
In search of their third world title, the U.S. team were comprehensively outplayed by the Brazilians in its worst defeat in any World Cup match.
The semifinal exit was a repeat of the 2003 event, when the Americans were eliminated by Germany.
Heartbroken
"We could have come out stronger I think but today was Brazil's day," American striker Abby Wambach said.
"I'm heartbroken.
"The first goal was kind of a fluke goal, then Marta comes down on the second goal and then we go down on the red card. Things were not falling for us today."
In the 20th minute, Formiga sent in a corner, which bounced just short of the goal.
Attempting to head it behind, midfielder Leslie Osborne put the ball between goalkeeper Briana Scurry and Lori Chalupny and into the back of her own net.
The selection of Scurry between the posts may well be a important note in the post mortem.
Scurry, playing in her 164th game for the U.S., was surprisingly picked ahead of Hope Solo, who started the first four games.
Solo had conceded two goals in the first match but hadn't been breached in the following 300 minutes, while Scurry, hadn't played a full game in three months.
Marta magic
But if Osborne was to blame for the first goal, the responsibility had to be shared for the second.
After 27 minutes, Marta evaded a half-dozen players before hitting a left-footed shot from 15 yards that hugged the ground and beat Scurry diving to her left.
The desperate Scurry got her left hand to the ball but couldn't stop it.
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| Team meeting: Brazil enjoy a group prayer after their victorious semifinal [GALLO/GETTY] |
Forced to push for the goal in the second half, the U.S. left itself exposed at the back with Maycon, Daniela and Cristiane narrowly missing in the opening minutes.
Cristiane finally broke through in the 56th to make it 3-0, left-footing a shot home in a one-on-one contest with Scurry.
"Tonight we played as a team, and we have not always done that," Brazil coach Jorge Barcellos said.
"We have the individual talent and this game was a complete team effort."
Restricted
The Americans had only two shots on goal in the first half and top striker Abby Wambach was a shadow of her best.
Kristine Lilly, playing in a record fifth World Cup, had the best U.S. chance in the second half but her point-blank shot landed in Andreia's hands in the 63rd.
After the third goal, Brazil slowed the play as the Americans kept pressing for a score.
Brazil's last flurry came in the 79th when Marta showed off all her talent.
Off the left wing, she faked around U.S. defender Tina Ellertson, raced into the box, dummied around another and beat Scurry with a shot that drew a huge ovation from a crowd of 48,000.
Brazil's victory was only its second over the United States in 23 games.
The South Americans now play Germany in the final on Sunday.