While hardly unexpected, the steamy Southeast Asian conditions have produced a number of surprising results, usually favouring the host nations.

"The biggest problem is the weather. The climate of Kuala Lumpur has brought the quality of matches down," said Iran coach Amir Ghalenoei.

Pre-tournament favourites Australia have been the biggest victims, held to a draw by Oman before being shocked 3-1 by war-shattered Iraq.

"It must be the heat when a country which reached the World Cup knock-out stages is left with one loss and one draw," mused Japan star Shunsuke Nakamura.

Australia defender Lucas Neill said most teams were struggling with the conditions.

"You look at the last 10-15 minutes of almost every game in the tournament and everyone seems to be wringing their shirts out and struggling and making a lot of changes," he said.

Despite night-time kick-offs temperatures have soared in the Asian capitals, reaching 37 deg C (99 deg F) at times accompanied by suffocating humidity.

Within minutes of the start players are often drenched in sweat and panting heavily, a sight more closely associated with the final stages.

"It's so humid and hot here in Jakarta that it's really hard for one player to play the entire 90 minutes," said South Korea's Lee Chun-Soo.

Co-hosts Thailand, Vietnam and Indonesia have all cashed in, confounding expectations to produce shock results against higher ranked opposition.

Teams like Iran and China have profited from special fitness programmes to prepare their players, while others have fallen by the wayside. Arab teams have been especially hard hit with Iraq and Saudi Arabia the only ones to win.

"When we arrived we had a special programme knowing Malaysia is a difficult climate with its high humidity. So we started with physical fitness training," said Iran's Ghalenoei.

"Some people in the media questioned that but we needed it with the Malaysian weather."

In the first 12 matches only four goals were scored in the last 10 minutes, underlining the difficulty of the conditions.

Jeff Steinweg, head of medical services for Football Federation Australia, said some players felt the heat more than others.

"We go to great lengths to ensure we keep the hydration up for the players," Steinweg said.

Australia's Mark Schwarzer revealed he lost three kilograms during the opening match -- and he's the goalkeeper.

"I lost three kilos and most of that was during the warm-up and I had to back off the warm-up because it was so harsh," Schwarzer said.

"Everyone has been losing two-and-a-half to three kilos each training session as it is, so then to look at a game situation where guys have lost up to five kilos it just goes to show how hard it was."

Japan coach Ivica Osim summed up the difficulties faced by everyone after his team's victory on Friday against United Arab Emirates in Hanoi.

"Most of all, I am happy that it has ended without any of our players and staff suffering a heart attack," he said.

"It was such harsh weather conditions."

The Asian Cup is being held in Southeast Asia for the first time since Singapore in 1984, when Saudi Arabia beat China in the final.