By Steve Keating

RIO DE JANEIRO (Reuters) - The United States reaffirmed their status as gold medal favorites on Wednesday with a devastating 105-78 defeat of Argentina to storm into the semi-finals of the Olympic men's basketball tournament.

Even though the United States were the only team to finish group play without a loss, questions about their ability to claim a third straight gold swirled after three unimpressive narrow wins to close out preliminary play.

'What was wrong with the United States?' basketball fans asked.

The answer? Nothing.

"We got our swagger back, offensively and defensively," declared Paul George to reporters after the United States ran their Olympic winning streak to 23 games.

With the United States looking vulnerable, the fourth ranked Argentines came into the quarter final thinking 'upset'. After all, they had done it before.

With a 135-5 record in Olympic competition, losses are rare at the Games for the United State but Argentina can claim one of them.

It came on the same stage 12 years ago at the 2004 Athens Olympics when Argentina beat the Dream Team in the semi-finals and then went on to take the gold.

That loss triggered an overhaul of USA Basketball, the men going unbeaten ever since.

But on Wednesday there would be no repeat against a motivated Team USA that clearly wanted to make a statement.

Kevin Durant has big say in the outcome leading the U.S. on the score sheet with a game-high 27 points while George had 17 and eight rebounds.

"The only thing that we changed was our passion and our energy," said Kevin Durant. "We were all one unit tonight and we need that going forward."

"We always felt we had another level to go to especially after the last three games in the pool play."

Things did not start positively for the United States as Argentina jumped out to a 19-9 lead, the seething, flag-waving pro-Argentine crowd erupting with each basket. Each missed U.S. shot drew an even bigger roar.

But with so much talent the United States were never going to go down without a fight.

Shifting gears the United States went on a 15-2 run to end the first quarter and then stayed on the gas in the second with an 11-0 dash to take control.

"I wouldn't call it relief, I just think we are evolving," said U.S. coach Mike Krzyzewski. "The last three games in the pool play were very beneficial to us because we played three outstanding teams.

"They showed some weaknesses that we had and we tried to get better."

The United States will now face Spain, 92-67 winners over France, on Friday for a place in the gold medal final.

The other semi-final will see Australia, who dumped Lithuania 90-64, take on the winner of Croatia and Serbia who play later on Wednesday.

(Additional reporting by Mary Milliken; Editing by Alison Williams and Andrew Hay)