"They are a completely new team with only the goalkeeper and four other players held over from our last game," said Osim.

"They are more aggressive and play modern football. They have a number of players whom we may find difficult to deal with," added the 66-year-old Bosnian, who led the former Yugoslavia to the 1990 World Cup quarterfinals.

Saudi Arabia, who last won the title in 1996 but failed to reach the knockout stage in 2004 for the first time in two decades, have shown solid form through the tournament, whipping Uzebekistan 2-1 in the quarterfinals.

They posted two wins and a draw in the group stage.

"We'll have a very, very big game as both teams are similar in style and powerhouses of Asian football," said Saudi coach Helio Dos Anjos, who has shaken up the squad after replacing fellow Brazilian Marcos Paquetta in March.

He said his side's loss to the Blue Samurai in November "doesn't matter at all."

"We are a new team and we have a chance to win," he said.

But Dos Anjos admitted his side was not as prepared as Japan after being forced to travel 12 hours from Jakarta following Sunday's quarterfinal to arrive here just 48 hours before the match.

In contrast, Japan have been in Hanoi for nearly three weeks and beat Australia on penalties in their last-eight match on Saturday, giving them plenty of time for rest and recovery.

"There is a problem in our preparation at the moment while other teams are having a rest," said Dos Anjos, who has had a long coaching career.

"But I don't speak about it. We will try our best to prepare and I hope our players will do well."

Yasser Al Qahtani leads the Saudi strikeforce alongside Malek Alhawsawi with Japan's hardman centre back Yuji Nakazawa tasked with keeping them at bay.

Osim said he had confidence in his back four.

"Our defenders are capable and I don't feel it necessary to change them," he said.

Japan and Celtic playmaker Shunsuke Nakamura said his side must stop the Saudis from launching lightening counterattacks, as they have done so successfully in the tournament so far.

"They charge forth all at once and go on to shoot," said the 29-year-old Scottish Player of the Year, whose free kicks helped Celtic win the Scottish Premier League title last season.

"We must check them tightly because I can picture a scene in which they come fighting all out with strikers and even defensive midfielders coming to the net."

Nakamura, who will link up with Frankfurt striker Naohiro Takahara on Japan's offensive, set up the sole goal in their defeat of Saudi Arabia 1-0 in the 2000 Asian Cup finals. Saudi Arabia also lost to Japan in the 1992 final.

"We need to mount fast breaks ourselves against their solid defence and attempt long-range shots in addition to our quick passwork," he added.

At stake for both sides is a place in the final in Jakarta on July 29 against either South Korea or Iraq who play their semifinal in Kuala Lumpur, also on Wednesday.