He did Friday against the Texas Rangers.
The right-hander gave up two hits in five scoreless innings and Hunter Pence and Andres Torres backed him with two-run home runs in a 5-2 victory in front of a sellout crowd of 12,106 at Scottsdale Stadium.
"I felt good in the bullpen (warming up before the game)," said Cain, who was 16-5 in 32 starts for the World Series champions in 2012. "I thought about where I wanted to throw. I was confident throwing whatever I wanted. The misses weren't as big."
Cain called Posey's throws to second "pretty ridiculous."
"Those guys can run. He backhanded the ball on the second one (before throwing," Cain said.
Cain knows he can help Posey keep baserunners off balance by varying his times to the plate and not allowing them to get a true read on his motion.
"You want to be around the plate to give him a chance," Cain said. "If you do that, it doesn't matter who is running. It will be close."
Veteran right-hander Derek Lowe, making a bid for a relief spot after being signed to a minor league deal by the Rangers on March 6, gave up two hits in two scoreless innings in his first start of the spring.
It wasn't that long ago, Lowe said, when he was throwing batting practice to his 9-year-old son's Little League team. He pitched for Cleveland and the New York Yankees in 2012.
Lowe, one of only three men in major league history with at least 160 victories and 80 saves, said he wanted to use his time against the Giants "to make an impression. As much as you want live BP to give you an idea, it can't duplicate what you can get in a game.
"The first inning was a little rough. The second inning was a lot better. I had a lot more control over where the ball was going."
After Lowe's departure, Pence broke a scoreless tie with a two-run home run off Wilmer Font in the fourth inning and drove in a run with a double in the sixth. Torres' two-run shot came off Johan Yan in the seventh.
RHP Sergio Romo, the Giants' closer, gave up a run on two hits and struck out a batter, pitching the seventh inning . . . the Giants made several roster moves on Friday. Six RHPs were sent to the minor-league camp, along with one LHP, three INFs and one OF. Three more RHPs were optioned to Triple-A Fresno, one LHP, two INFs and two OFs. One LHP went to Class A Advanced San Jose. ... The Rangers will travel to Las Vegas for split-squad games on Saturday and Sunday against the Chicago Cubs. RHP Nick Tepesch is scheduled to start Saturday and LHP Robbie Ross on Sunday. The other games will be against the Los Angeles Dodgers in Surprise, Ariz., on Saturday and the Seattle Mariners in Peoria, Ariz., on Sunday. ... Rangers RHPs Joakim Soria (Tommy John) and Colby Lewis (surgery for torn flexor tendon) threw bullpens on Friday.