Tom Kite and Kermit Zarley share fourth place at 6-under par, followed by Jim Ahern, who is alone sixth after posting a 5-under-par 67 in Friday's opening round at Silverado Resort's South Course.
Doyle wasted no time in breaking into red figures. He drained a 12-foot birdie putt at No. 1 and recorded back-to-back birdies at four and five. Doyle knocked a 6-iron to a foot to set up the kick-in birdie at eight and he closed his front nine with a two-putt birdie at the par-5 ninth.
Doyle, the 2001 Player of the Year, continued his fine form on the second nine. He stuffed his approach five feet from the hole to birdie the 10th and made it four in a row with a three-foot birdie putt at the 11th.
The 54-year-old had one birdie left in his bag. Doyle missed the green short at 18, but chipped his third five feet from the hole. He converted the birdie opportunity to clear himself from the field and take the lead.
'I had a flawless day, really,' said Doyle, who is winless in 2002. 'I didn't miss a fairway and hit 15 greens. Everything came pretty easily. Today was really perfect.'
Rachels used a back-nine surge to move into second place. He tallied two birdies on the front side, but birdied his first three holes on the second nine.
He ran home a six-foot birdie putt at the 14th, but hit a poor chip at No. 15 and dropped a shot. Rachels converted a 10-foot birdie putt at the 16th and closed with an 18-footer for birdie at the last.
'Nobody is more surprised than I am,' said the defending champion. 'I actually didn't hit the ball very good on the front nine. It's cool when things go your way.'
Fleisher collected three birdies in a row, two times, once on each nine. Like the other players near the top of the leaderboard, Fleisher two-putted for birdie at the closing hole.
'The scores will be low unless winds come up and temperatures cool,' said Fleisher. 'The field has a tendency to come back. There are lots of birdie opportunities.'
Jim Colbert, Doug Tewell, Walter Hall, J.C. Snead, Gary Player, Jim Thorpe, Stewart Ginn, Ed Dougherty and Tom Purtzer share seventh place at 4-under-par 68.
Full-field scores from the Napa Valley Championship