Hunter Strickland (.270) and Neil Ramirez (.300) were more vulnerable.
But Giants manager Bruce Bochy maintained confidence in all of them.
"I'm not just sitting on the fence," Bochy said before Sunday's season opener against Arizona. "That's why we went this way. We're comfortable with all our righties against lefties."
San Francisco's lone bullpen lefty, Ty Blach, held left-handed hitters to a .130 average in his four big league appearances last season.
Bochy sounded particularly upbeat about Law, due primarily to his pitching style.
"He's a four-pitch guy with velocity, two breaking balls and a changeup.