The 15-time major champion, making his first appearance since knee surgery in August, tops the leaderboard alongside compatriot Gary Woodland on six under.

His round began with three successive bogeys but the 43-year-old fought back with nine birdies in 15 holes.

"I wasn't expecting to shoot six under par after that start," said Woods.

Woods and Woodland lead home favourite Hideki Matsuyama by one shot at the Accordia Golf Narashino Country Club in Chiba.

It was Woods' lowest season-opening score of his career as he chases his 82nd US PGA Tour victory to tie the all-time record held by Sam Snead.

"It was ugly early and it was nice to be able to flip it and really get it going," said Woods, who won his 15th major at the Masters in Augusta in April.

"Now I'm in a position where we're going to have a long, long weekend of a lot of golf that hopefully I can keep it going."

Paul Casey is the leading Englishman after carding a one-under 69 to sit tied for 14th, five shots off the lead.

World number two Rory McIlroy is eight shots off the pace after struggling to a two-over 72.

It was an even worse day for fellow Northern Irishman Graeme McDowell, who is bottom of the leaderboard after carding four bogeys, two double bogeys and one triple bogey in his 11-over-par round of 81.