But this day, that wild child of the early campaign resurfaced, with his inconsistency and erratic offerings.
It didn't help the Giants' cause that Barry Bonds was pulled from the game after two innings with a sore left knee -- yes, the other
knee -- and save for Steve Finley's solo homer and RBI double, San Francisco could do little offensively against A's starter Esteban Loaiza, who scattered six hits in his first complete game since 2004.
"I felt like I was just missing," said Cain (6-6). "I got myself in trouble, and they were able to capitalize on it. So often it's going to kill you, no matter what you do. I put myself into trouble just about every inning except for the second."
Manager Felipe Alou allowed that rookies will have rough times -- good games then poor ones -- until they get more experience and stabilize their outings.
Cain knows it, too, but he admitted there was frustration against the American League West division leaders, feeling he wanted to jumpstart a Giants' winning streak and had the tools to succeed.
Instead, there were more balls than strikes and more balls hitting bats than anticipated.
"I couldn't get that put-away pitch, and they were real patient and able to end up working the count into their favor a lot of times, too," said Cain, who threw 105 pitches while giving up two runs in the first, third and fifth frames.
Even reliable bullpenners Brad Hennessey and Jeremy Accardo gave up runs in the latter innings -- they, too, experienced one of those days.
Still, Cain expected more from himself, and part of the frustration came from feeling solid, throwing good stuff, but with bad results.
"My fastball velocity wasn't the same [as the last time he faced the A's], but I felt like I threw all four pitches a lot better today," he said. "It didn't end up showing, but I felt like I had all four pitches today.
"It might have been [the high pitch count], or I might have just had a bad day -- an off day, I don't know," said the right-hander.
While he was hardly pleased to see the Giants lost, Finley could finally relax after smoking -- believe it or not -- his first home run at AT&T Park after 256 previous at-bats.
Finley knew AT&T Park was a gap-hitters' park and seven of his eight triples this season have been hit there, and he was wondering if the ball would ever leave the park.
"I was beginning to wonder, but sooner or later it was bound to happen," said Finley, who has five homers this season. "It was a ball I've hit lots of other places and been way out somewhere else, but I just knew it would go out."
Finley said Loaiza wasn't doing anything special, but he kept the Giants hitters off balance.
"He was mixing in a cutter and changeup, and we were just hitting balls at people -- we were hitting 'em hard," said Finley. "They just didn't find any holes."
San Francisco, now 37-38, unable to win more than three consecutive games and struggling to climb higher in the NL West standings, needs to get a streak soon. Finley still believes it can happen.
"We're just waiting for that good stretch," said the veteran. "It seems like we've been treading to hold our head above water this whole season, with different guys going down with injuries. We've never had a run of people being healthy. Once we get that, that'll be our time to run."
San Francisco has Monday off and begins a three-game series against the Texas Rangers on Tuesday night at AT&T Park to conclude Interleague Play.