Thatcher, a former Auburn star in his first season on the PGA Tour, birdied his first four holes Thursday en route to a 6-under-par 66. His 30 on the front nine tied the record at the $3 million tournament at Montreux Golf and Country Club on the edge of the Sierra Nevada.
Calcavecchia, Scott Simpson, Mark Wiebe, Mark Wilson, Vaughn Taylor and Daniel Chopra all finished at 67. Corey Pavin and Rich Beem were at 68.
A rain delay of more than four hours forced half the 132-player field to complete first-round play Friday morning. Calcavecchia birdied his first two holes to get to 7 under par before he made double bogey on the 464-yard, par 4 eighth hole.
Calcavecchia, the 1989 British Open champion, had come within a foot of a hole-in-one on his last hole before darkness caused played to be suspended Thursday.
Thatcher hit his approach shots inside 10 feet on each of the first four holes -- twice within about two feet -- and got to 7 under when he made a 9-foot birdie on his 12th hole of the day.
'It's definitely the kind of start you dream about,' said Thatcher, who has made just four cuts in 14 events this year. His best showing was 68th in the BellSouth Classic in April.
Thatcher, who won the Nationwide Tour's Bank of America Monterey Peninsula Classic in 2002, made a 15-foot birdie putt on his last hole at the PGA Tour qualifying tournament last year to earn his tour card.
He barely missed qualifying in 2001, his first year out of college. He needed a par on the last hole at Q-school, but his approach shot cleared the green, hit the cart path and bounced onto the roof of a three-story clubhouse.
'It was real disappointing, but at the same time I probably needed the two years I was on the Nationwide Tour,' he said. 'And I've definitely had some vindication, so to speak. Needing a par to win and not getting it done and needing a birdie to win and getting it done sort of balances out.'
Wiebe had five birdies in a bogey-free round that he called one of his best since surgery on his left elbow in 2001.
'Shooting 5 under is great, but I'm more pleased that since coming back from surgery I've been watching my game come together,' he said.