Schwartzel, last year's runner up, shot three birdies and an eagle to go along with a bogey for an overall 18 under 198 at the Amata Spring Country Club, staying on track to end a victory drought that stretches back to his Masters win in 2011.
"I feel comfortable playing this golf course," Schwartzel said. "That's the biggest key is just feel comfortable whatever you do. If that means being aggressive, then that's being aggressive."
Chopra, who started the round four strokes back, rallied after a double bogey on the fifth for a 69.
"I played fairly well. I had a couple of loose shots but nothing was really too bad," said Chopra, a two-time PGA Tour winner. "I'm five behind. Obviously, my goal is to go out there and try to make it uncomfortable for Charl. Nobody wants to see him run away with it. I want to do my best to make it close down the stretch."
Twenty-five players finished their second rounds Saturday after darkness ended play on Friday.