Kuramoto, who had 34 career victories in Japan but is in his first season on the Champions Tour, started on the back nine at the TPC at Snoqualmie Ridge course and was five-under at the turn. He then opened with an eagle on the par-five, 554-yard No. 1 hole. That was set up with a three-iron second within two feet of the pin.
He took sole possession of the lead with a birdie on the par-3, 226-yard No. 6 hole then added another birdie on No. 8 to match the course record. He had the fewest putts among the 78-golfer field.
David Edwards, also in his first year on the Champions Tour, is second after shooting 7 under.
Kuramoto, who was the Tour Q-school medalist this year to earn his playing card, has played in 17 tournament this season with just three top-10 finishes. He said a body turn tip Tuesday from J.C. Snead made the difference.
'I didn't have confidence coming in here,' he said. 'Not until I got the tip.'
He added that the 7,120-yard TPC course is not set up for his game 'but I just think about hitting fairways and greens and making putts. I don't care about the scores.'
Edwards won the 3M Championship two weeks ago.
'Being young (50) out here is an advantage. That's the first time it has been that way,' Edwards said. 'You know coming out here your first few years ought to be your best years. I come out here with that in mind. When you're going well, you need to ride it and get all you can out of it.'
Andy Bean, Keith Fergus, Mike San Filippo and Australian Graham Marsh were tied at 6 under.
Bean birdied his final two holes. Fergus birdied three of his final five holes, holing out his last, the par-3, 207-yard No. 9, with a chip from the sand. San Filippo shot a five-under 31 on the front nine. Marsh dropped four shots to par on his back nine.
Marsh has six Champions Tour wins but none since 1999. Asked if he's capable of winning again, the 62-year-old Marsh said, 'Just take a look at the tour statistics and see where the winners come from.'
Indeed, in 811 events in the Tour history, players who were 60 or older have won only 15 times.
'Of course, one of the reasons I continue to play is to have the opportunity to win again,' Marsh added. 'In a positive sense, I'm still playing because I still feel I have a chance. What's my chances? Just look at the statistics.'
The conditions were nearly perfect for low scores, very little wind, soft, consistent greens and mild temperatures. 'I wouldn't be surprised to see a guy go really low this week,' Marsh added.
Kuramoto, who also had 58 starts in the 1980s and '90s on the PGA Tour with four top-10 finishes, had open-heart surgery six years ago to restructure his mitral valve. His wife, Margie, said doctors told him that the surgery probably came 'right before heart failure.'
'My dream was to play on the Champions Tour,' said Kuramoto, with his wife interpreting. 'If I wanted to do that, I definitely had to have the operation. After that, I felt good.'
He felt good enough to shoot a 59 in a 2003 tournament on a Jack Nicklaus-designed course in Japan. Snoqualmie Ridge also is a Nicklaus design.
The Golf Channel will televise all three rounds beginning Friday at 4:30 p.m. ET.