Charles Howell III reached 4-under on his round with a birdie at the 17th, but he bogeyed the last to fall back into a tie for second. Howell was joined by Brad Faxon, Glen Day, Tom Byrum and Kelly Gibson at 3-under-par 67.
Tanaka found trouble early on at Hamilton Golf & Country Club with a bogey at the par-4 third but he managed to recover at the very next hole. He hit his third shot at the par-5 fourth to five feet for a birdie and knocked a 5-iron inside 10 feet for another birdie at the par-3 eighth.
'I knew that good management is important on this course,' said Tanaka. 'So I just concentrated on how to put the ball on the fairway and to be patient.'
The 32-year-old continued his fine play on the inward half with a birdie at the 11th and made it two in a row after his approach landed within three feet of the cup at the par-4 12th.
Tanaka then gave himself another opportunity for a birdie at the par-5 17th. He left his second shot well short of the putting surface but hit a sand-wedge to five feet for a birdie to secure the early lead.
'The fairways are very undulating and very tricky,' said Tanaka, whose best finish this season is a tie for sixth at the Reno Tahoe Open. 'But when I play, I just am trying to play well. So it really doesn't matter, a new course or an old course.'
Gibson played the back nine first and tallied birdies at the 15th and the 17th to move to minus-2. Gibson added a birdie at the fourth to finish one shot off the lead.
'It's a great golf course,' said Gibson. 'You have to have everything going right, you have to hit good drives, a lot of quality iron shots.
Tom Lehman, Willie Wood, Tom Pernice, Jr., Patrick Sheehan, Tommy Armour III, Jeff Brehaut and Bill Glasson finished two shots off the pace at 2-under-par 68.
Local favorite Mike Weir, who has never finished in the top-10 at this event, picked up two birdies and a bogey on the front side to make the turn at minus-1.
The reigning Masters champion hit his approach to three feet for a birdie at the par-4 10th but found trouble with a bogey at the 15th. Weir then converted a short birdie putt at the 17th before stumbling home with a bogey at the closing hole.
'Overall, I felt good out there,' said Weir, who finished with a 1-under-par round of 69. 'I think when you feel comfortable on a golf course, the scores are going to come with that.'
John Rollins, who earned his first career victory on the PGA Tour in a playoff at this event last year, struggled with three bogeys and a double bogey for an opening round of 75. Vijay Singh, the fourth-ranked golfer in the world, also struggled with a 75 on Thursday.