HANOI, July 14 - Japan have begun to float like butterflies -- and sting like mosquitoes, midfielder Shunsuke Nakamura said in a Muhammad Ali-like warning to their Asian Cup rivals.

The holders produced an easy 3-1 win over United Arab Emirates despite Hanoi's suffocating humidity on Friday to go top of Group B ahead of co-hosts Vietnam on goal difference.

"The first 20 minutes is the hardest. Both teams are on a level footing in the heat," Nakamura told Reuters after Japan had rebounded from a lacklustre 1-1 draw with Qatar in their opener.

"After that it's a question of who throws the best jab. We gradually started doing that and got on top of them by passing the ball around nicely.

"We wore them out and delivered a straight knockout."

The Celtic midfielder has made light of the clinging Vietnamese heat and swarms of mosquitoes to become the driving force of the Japan team.

The 29-year-old has also helped ease the tension inside Japan's squad with Bosnian coach Ivica Osim's grumpiness and fits of pique threatening to become a distraction.

While Osim prowled around Japan's training pitch muttering furiously and waving his arms in frustration, Nakamura bared his backside to hoards of media to show off a nasty mosquito bite.

DIPLOMATIC EXCUSE

He even diplomatically offered a ready-made excuse for Australia's struggles in their first Asian Cup following their 3-1 defeat by Iraq in Group A.

"The heat will be hard on Australia," said Nakamura, scorer of Japan's third against UAE from the penalty spot.

"They're not used to the heat and they have a lot of muscle to carry around."

Japan have won the last two Asian Cups in similarly hot and humid conditions, lifting the trophy in Lebanon in 2000 and again in China in 2004.

Osim's side will start as clear favourites to finish top of Group B when they face Vietnam in their final first-round game on Monday -- by which time Australia could be out.

"Australia got the last 16 of the World Cup and look at them," Nakamura said.

"The heat is the unique thing about the Asian Cup.

"If we can keep playing at this sort of pace I think Japan will do alright!"