Playing in a steady downpour at the Phoenix Country Club, Woods opened with a birdie on the par-4 10th hole and added four more to take the lead in the $1.89 million tournament, the richest on the Japanese tour.
'I don't remember leading after the first round of any tournament this year,' said Woods, who teed off from the 10th. 'Obviously, this is a very positive start.'
Kaname Yokoo of Japan was second. Compatriot Hideto Tanihara, South Korean Kim Jong-duk and Australian Craig Parry carded 69s.
Woods, who lost his No. 1 ranking to Vijay Singh this year, is looking for his first win in Japan.
He finished eighth in this tournament two years ago. His other appearances in Japan include a 15th-place finish at the Casio World Open in 1998 and a second-place outcome at the 2001 World Cup, when he paired with fellow American David Duval.
On the par-4 14th, Woods hit a 7-iron left of the green on his second shot, then chipped in from 50 feet for his second birdie of the day.
'I was just trying to get the ball close,' Woods said. 'I was looking to get out of there with a par and was lucky to make birdie.'
Woods, who also had birdies on Nos. 16, 2 and 8, said he wasn't thrown off by the bad weather.
'I grew up in Southern California, but on the few days there was bad weather, I would always go out and practice,' he said. 'That allowed me to play well in bad conditions.'
Going back to the 13th hole of the 2002 Dunlop Phoenix, Woods is now bogey-free in 23 holes on this course.
'Anytime you can play this course without a bogey it's a good day, especially in these conditions,' Woods said. 'The greens weren't consistent. In low spots the putts were slow, in high spots they were fast so it was tough.'
British Open champion Todd Hamilton of the United States struggled with the wet conditions and finished with a 73 that included five bogeys.
Defending champion Thomas Bjorn of Denmark shot a 75.
Bjorn will be looking to tie the record of three Dunlop Phoenix titles held by Japan's Jumbo Ozaki, but sits 10 strokes off the pace.
Bjorn beat Spain's Sergio Garcia to win this event in 1999, and defeated Garcia again last year by coming from behind on the final day.
Woods feels confident heading into the next three rounds.
'Obviously, it still early,' he said. 'You've got to be patient but that's one of the attributes I feel I have, one of the things that's allowed me to win as many tournaments as I have.'
The last time Woods won a stroke-play tournament was the Western Open in July of 2003.
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