TWO of the world's most experienced marathon drivers clash head on for the first time in Asia's premier endurance event - the 555 Hong Kong to Beijing Rally - which starts today with a ceremonial flag-off at Ocean Terminal. Vying to be the first to reach the Great Wall of China are former world champion, flying Finn Ari Vatanen and Japanese rallying legend Kenjiro Shinozuka. Vatanen has won an amazing four Paris-Dakar rallies, the world's premier marathon event, and Shinozuka has competed six times, finishing third to the Finn in 1987 and second in 1988. But in past Paris-Dakar races Vatanen and Shinozuka have competed in vastly different vehicles. The Japanese driver favoured Mitsubishi Pajero four-wheel-drives on each occasion, while Vatanen had specially adapted, and more nimble sedans. ''It will be the first time we have competed in an endurance rally with similar vehicles,'' Shinozuka said. The Japanese, who has been rallying for 25 years, will be behind the wheel of a new Mitsubishi Lancer while Vatanen will drive a Subaru Legacy. ''I'm looking forward to the challenge but Ari must be the man to beat. He has a young and active mind but an old head,'' said Shinozuka. But 41-year-old Vatanen has reason to take care, too. He must watch 44-year-old Shinozuka, and his two 555 Subaru World Rally Team teammates, Colin McRae and Possum Bourne. McRae posted Subaru's only victory in the World Championship this season in New Zealand. And New Zealander Bourne is the top rally driver in Asia and will be determined to defeat his world-rated rivals. Shinozuka believes that reliability could be the deciding factor in the 3,800-kilometre journey to Beijing which features 559 kilometres of special stages spread over seven days. But Vatanen has another advantage - he competed in the last Hong Kong to Beijing in 1987. ''But I prefer to forget that race, I had an accident with a very small tree,'' he said yesterday. That small tree ended Vatanen's race. The serious business begins this afternoon with a super-special stage at the Honey Lake Resort in Shenzhen.