The 27-year-old right-handed pitcher made 12 starts for Cincinnati last season after returning from right elbow surgery in August 2009.
"Volquez is very confident, plus we think he can handle it," Baker said Tuesday. "Not much bothers him."
Volquez opened the National League playoffs against Philadelphia last year, losing as Roy Halladay threw a no-hitter.
"They gave me the opportunity to be the No. 1 one here," Volquez said. "I'm very happy about that. I'll take it."
"We wanted to break up Volquez and Cueto so they don't try to out-radar-gun each other," Baker said.
Aaron Harang, who signed with San Diego this offseason, was the Opening Day starter in Cincinnati the previous five seasons.