BUENOS AIRES, Argentina (AP) _ The sights and the sounds favored Argentina from the beginning, even if tradition didn't. After half an inning, the hometown team also had control of the game.

And it held it for one of the biggest upsets in Pan American Games history. Argentina, basically a stranger to baseball, beat the United States 6-4 at the game invented by Americans.

The victory was extra sweet for manager Carlos Siffredi, who has spent five years putting this team together and taking it around the globe to train.

``It's been a long process and now there's a lot of pride,'' Siffredi said. ``It definitely helped a lot to play at home.''

The U.S. team, represented by St. John's University, didn't waver. With theirs ears ringing from crackling fireworks, thumping drums and buzzing whistles, the Americans began fighting back from a big hole.

A five-run deficit was whittled to two and an inning later it was down to one. They couldn't get any closer, though, as Argentina's starter got stronger in the middle innings and protected the lead.

While it was a huge victory for Argentina, a country with little baseball tradition and no professional leagues, for the Americans it was a disappointing way to begin the tournament _ and a good lesson in how hard it is to represent a nation.

``The noise was incredible,'' said USA starter Mike Maerten. ``I'd say it was the biggest crowd I'd ever pitched in front of. There were a lot of adjustments to make.''

There were many pent-up emotions being released by the hometown crowd of about 4,000 at Ezeiza Stadium. . This was the first time in seven years the national team played here and it was the country's first Pan Am appearance since the tourney debuted in 1951. Argentina lost all of its games that year.

The loss leaves Team USA with a lot of work. It must win at least two of the next three games, against Mexico, Puerto Rico and Guatemala, to assure advancing to the medals round.

Not doing so would be a huge disappointment. In 11 tournaments, the United States has taken home 10 medals.

``This means we've got to come back further,'' said St. John's coach Joe Russo. ``It's always tough to come out of the losers bracket. We've just got to improve as we go along.''

They knew from the outset that Saturday would be tough as they looked into the stands of the 6,000-seat stadium and heard the rumble from behind the Argentina dugout.

Fans brought all sorts of noisemakers: Cannons, drums, fireworks, guitars and whistles. They added to the partying by chanting pep songs.

There was plenty of reason to cheer from the beginning.

Argentina's first four batters singled and the next two walked. The Aregentines scored five times in the first inning and still had the bases loaded when the side was retired.

By the late innings, the crowd became even more demonstrative. Many fans were standing, waving their T-shirts like rally towels and swirling their blue-and-white flags.

Some of the loudest wails came in the eighth inning, when Argentina scored for the first time since the first inning, and again in the bottom of the eighth, when an American was thrown out at the plate for the final out.

Then, when 36-year-old reliever Miguel Rodriguez got the last out, there was as much hugging and screaming as if Argentina had just won a World Series.

Throughout that celebration, all the disheartened Americans could do was stand with their hands on their hips waiting to slap hands with the victors.

They knew they had made a nice comeback, getting three runs in the bottom of the first and another in the second, yet there was the bitter disappointment of beginning the tournament with a defeat.

``It's not embarassing,'' said Chris Lemonis, one of the hitting stars with a single, a double and two RBIs. ``It's a loss. We'll bounce back.''