Japan's dead-ball prowess could hold the key to breaking down Paraguay's stingy defense as both World Cup underdogs chase a first appearance in the quarter-finals.

The South Americans conceded just once in the group phase, while Japan advanced thanks to a pair of precision free kicks from Keisuke Honda and Yusuhito Endo clinching a 3-1 victory over Denmark.

"Obviously from what we saw the other day, we need to try not to concede fouls near the area," Paraguay coach Gerardo Martino said ahead of Tuesday's last-16 meeting in Pretoria.

But the Japanese fear they may have become too predictable and are wary that Paraguay has had more time to study their set piece techniques.

"One thing we will have to try and do is vary our set pieces to surprise them," Japan defender Tulio warned.

Japan's speed, though, is also not being underestimated by the Paraguayans as it helped the team upset the odds by beating both Cameroon and Denmark in Group E, while only losing to the Netherlands.

"Fundamentally they are a team who get back into their defensive positions very well, using a back-line of four and practically five midfielders, with Honda generally up front," Martino said.

"When they get the ball they come out very quickly on the counterattack, this is what we have to be careful of most, the fast breaks.

"When they find space they get men forward into attack and this is the most important issue to be careful about."

Paraguay surprisingly topped Group F after Italy's collapse despite drawing with the defending champions and New Zealand while only beating Slovakia. The goal conceded in the 1-1 draw with Italy was the only time the Paraguayan defense was breached in the group phase.

And Japan coach Takeshi Okada has warned that Paraguay has "a very solid defense, press as a unit and have fast transition from defense to offense."

Japan, though, has struggled in previous tournaments against South American teams, losing 1-0 to Argentina in 1998 and experiencing a 4-1 collapse to Brazil in 2006.

This is the first time Japan has reached the last-16 since 2002 when it co-hosted the tournament. And the east Asian nation is the continent's last surviving contender, with South Korea already removed by South American opposition, Uruguay, in the last-16 phase.

While the spotlight in South Africa has been on the poor performances on African teams on their own continent, Asian teams have again failed to make their mark on the world's biggest football tournament.

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