Australia take on Lionel Messi's Argentina in a David v Goliath World Cup showdown while the United States look to ambush the Netherlands as the World Cup knockout rounds get under way on Saturday.

After a group stage full of twists and turns, the business end of the tournament kicks off with 16 teams dreaming of plotting a path to the final in Doha on December 18.

The USA and the Netherlands open the second round at the Khalifa Stadium on Saturday, with the Americans aiming to advance to the quarter-finals for the first time since 2002.

Coach Gregg Berhalter's USA squad booked their spot in the last 16 with a 1-0 win over Iran to secure second place in Group B behind England.

While the Dutch possess the greater historical pedigree, reaching three previous World Cup finals, the USA head into the knockout rounds brimming with confidence.

"It's a great opportunity, but it's not something that we're going into it thinking it's an honour," Berhalter said.

"We deserve to be in the position we're in."

The US face a Dutch team who finished first in Group A ahead of Senegal, Ecuador and Qatar without really showing their best form.

The Netherlands' veteran coach Louis van Gaal is wary of the threat posed by the energetic Americans, describing Berhalter's team as one of the best in the tournament.

"They have an excellent team, I would say even one of the best teams," said Van Gaal.

"It'll be a tough match but it's nothing we can't overcome. We also have a good team.

"But I'm not going to downplay the USA. I think they're an example of what a good team is."

In Saturday's other knockout game, South American giants Argentina face an Australia side who confounded all expectations by getting out of a Group D that included defending champions France, Denmark and Tunisia.

However Argentina coach Lionel Scaloni is not ready to take anything for granted having already seen his team suffer a shock loss to Saudi Arabia earlier in the tournament.

"Whether or not they are inferior to us remains to be seen. I don't agree that they are. This is football -- eleven against eleven," Scaloni said.

"Forget who is theoretically favourites and let's play football."

Australia coach Graham Arnold meanwhile said he expects the Socceroos to raise their game once more against the star-studded Argentines.

"I just think that Argentina bring the best out of Australia. Our performances every time against Argentina have been very strong and very good," Arnold said.

"Playing against that type of talent, and that name I think resonates right across the world -- it's a football nation and it is inspiring to play against them."

Last-gasp Korea 
The group phase ended in dramatic fashion on Friday when South Korea reached the knockout phase with an injury-time winning goal against Portugal to set up a meeting with mighty Brazil.

With the clock ticking down at Education City Stadium, the Koreans knew they needed one more goal against Portugal to leapfrog group rivals Uruguay, who were facing Ghana.

Tottenham forward Son Heung-min produced a brilliant assist for Hwang Hee-chan to score the goal that secured a 2-1 victory.

The Korean players then watched the final minutes of Uruguay's match on a mobile phone as they waited for their place in the last 16 to be confirmed.

Uruguay, leading 2-0 against the Africans, needed one more goal to go through but fell agonisingly short despite piling on the pressure, crashing out by virtue of goals scored.

Korea's Tottenham forward Son said he was crying "tears of happiness".

"There were moments when I wasn't able to do my best and I am thankful for my team-mates that they were able to cover me in the moments I wasn't able to fulfil my duties. I'm very proud of them."

Uruguay veteran Luis Suarez in contrast sobbed in disappointment after the South Americans were eliminated.

Switzerland edged a bad-tempered encounter with Serbia to progress, winning 3-2 to earn a meeting with Cristiano Ronaldo's Portugal.

Remo Freuler smashed a half-volley into the net for the 48th-minute winner.

Tempers flared in the second half after Serbia appealed for a penalty, with the stadium announcer calling for an end to "all discriminatory chants and gestures" around 15 minutes later.

"I can't tell you the reason why and what happened exactly," said Serbia coach Dragan Stojkovic.

"Sometimes the tensions come and some maybe bad words can create some uncomfortable behaviour, but it's nothing special. It's normal, let's say, for this kind of game."

Brazil won Group G despite dropping nine players from their starting lineup and losing 1-0 to Cameroon with Vincent Aboubakar heading in a stoppage-time winner to claim a memorable win that could not prevent the African side being eliminated.