Brazilian striker Alexandre Pato, whose early performances prompted comparisons with Ronaldo and Pele, has failed to live up to his reputation at the Olympics and now finds himself on the sidelines.

The AC Milan player arrived in China as one of the big names of the Olympic tournament alongside Ronaldinho and Lionel Messi but has barely made a mark, scoring one goal in three group games and offering few attacking options.

Brazil's Pato warms up during a training session ahead the 2008 Beijing Olympic Games men's football semi-final round in Beijing on August 18, 2008. Brazil will play against Argentina on August 19. [Agencies]

He then lost his place to Rafael Sobis for the 2-0 quarterfinal win against Cameroon and, judging by the comments of coach Dunga, is unlikely to regain it very soon.

The 18-year-old, who has already seen action with Milan and Brazil, was expected to thrive in the Olympics, an under-23 tournament with three over-age players allowed per team.

But Dunga's praise of Sobis, who helped Internacional win the South American Libertadores Cup in 2006, appeared to be just as much veiled criticism of Pato.

"I opted for Rafael Sobis because of the way he has improved in training and during the games," said Dunga, whose team faces Argentina in Tuesday's semifinal.

"Rafael is a player who can survive tough marking, who opens up spaces, who can make diagonal runs and doesn't get caught offside.

"He gets involved in training and he is used to these types of games in the Libertadores."

Magical Messi

In sharp contrast, Argentina has a lot of pride in its talented star Lionel Messi.

Players and coaches heaped praise on the Barcelona striker after he steered defending champion Argentina into a glamor Olympic semifinal against Brazil.

The influential 21-year-old, considered by many to be the best player in the business, was instrumental in driving his side through a tough test against the Netherlands 2-1 in their quarterfinal.

Messi, who almost didn't play here with his club wanting him back in Spain in time for the Champions League third qualifying round matches, scored the first goal and set up the second for Angel di Maria in extra time.

"He is one of the best football players in the world," said Argentina coach Sergio Batista.

"The whole team had a great performace in the match. We won the game because of the endeavor of the team."

Even Dutch coach Foppe De Haan was full of praise, and tipped Argentina to beat Brazil on Tuesday.

"I like Messi, even though he's on the other team," he said. "When he gets the ball he is unbelievable. Argentina are better than Brazil, they have a modern passing game."

Like Argentina, Brazil needed extra time to beat Cameroon 2-0 with Rafael Sobis chipping the goalkeeper to break the deadlock.

Real Madrid's Marcelo made it safe with the second goal four minutes later after lead-up work by AC Milan's Ronaldinho and substitute Thiago Neves.

Brazil has won the World Cup five times but has never managed Olympic gold, something its players are desperate to put right.

As they work on a plan to shatter Brazil's dreams once again, Argentina will consult the legendary Maradona on how best to approach the game.

He arrived in China on Saturday to get behind the team, watching from the VIP box as Argentina beat the Netherlands.

Brazil has now scored 11 goals in four matches and has yet to concede a goal in the Beijing tournament, adding to Argentinian concerns.

In the other semifinal, Nigeria plays surprise package Belgium, which sent European powerhouse Italy packing 3-2.

Agencies/AFP