Langer, the 2008 winner, holed an 8-iron from 143 yards for an eagle on the par-4 sixth hole in his bogey-free round at Newport Beach Country Club.
"I played solidly all round," Langer said. "The only trouble I had was 17, but I got it up and down from a bunker to save par."
Clampett birdied three of the last four holes and finished with eight birdies and two bogeys. He holed a 30-foot birdie chip in the sixth hole.
Browne also birdied the par-5 18th, and had just 27 putts.
"I don't think I had but one chip the whole day," Browne said. "I basically hit every green."
Fred Couples, the 2010 winner, had a 67.
Defending champion Nick Price shot a 70. He opened with a career-best 60 last year.
Heavy rain is expected Saturday and Sunday.
"Everyone knows it's going to be cold and wet," Browne said. "Every shot you made was one less you have to try and make up in bad conditions the next couple days."
Langer, who now lives in Florida, isn't looking forward to the weekend weather.
"I used to be a good bad weather golfer," Langer said. "When guys were complaining about the weather, I was grinding it out. I certainly don't like playing in the rain now."
Clampett is happy to just be playing. After spending many years working in the broadcast booth, he has been able to get sponsor exemptions for tournaments.
"For me it was 15 years that I was away from the game," Clampett said. "I was really looking forward to turning 50 because my passion for the game is back. I wanted to play."