SCOTTSDALE, Ariz. -- Reviving a high school custom, Matt Cain has switched jersey numbers from 43 to 18, which formerly was worn by outfielder Moises Alou.

That's merely a cosmetic change. In 2006, his first full Major League season, Cain reclaimed a more essential teenage trait -- his attitude -- which has accelerated his already precocious development.

Cain's progress has fueled the Giants' belief that their starting rotation could be their chief asset. It's even permissible to speculate that Cain, not $126 million left-hander Barry Zito, might emerge as San Francisco's ace as the season unfolds. This is largely because Cain, 22, has proven that he can enhance his skills with a veteran's approach.

"It's always interesting to see a guy who has pitched a full year come back that next year," Giants right-hander Matt Morris said Thursday after the opening workout for pitchers and catchers. "A young guy like him, he'll soak up so much and then when the offseason hits, a lot of it really makes more sense. I'm interested to see how dangerous he's going to be. The sky's the limit."

The sky appeared to be falling for Cain after he began last season 1-5 with a 7.04 ERA in his first seven starts. What happened next has been well-documented: Cain skipped a start, threw two perfect innings in relief May 16 at Houston to reacclimate himself to pitching, then fired a one-hit shutout at Oakland on May 21. Those outings propelled Cain to a 12-7 record and a 3.34 ERA in his final 24 appearances.

"It kick-started a new time for me," the right-hander said.

Correcting a mechanical flaw at this juncture helped Cain improve. But a mental adjustment might have been more crucial.

"I actually started playing the game again and had fun with it," Cain said. "I kind of got back to being comfortable in the atmosphere I was in and calmed down."

Among the teammates helping Cain was Morris, who imparted a basic message: Keep it simple.

"Pitching can get so technical and you can think about every movement you make, but usually the best thing for guys like us who've done it all our lives is to forget about it all and let muscle memory take over," Morris said. "The more you think, you're slower and you get in trouble."

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"I tried to keep that [mind-set] the rest of the the time," Cain said. Before, he admitted, "I fought myself, probably trying to do too much at first."

Once Cain got over himself, opposing hitters became easy to subdue. He allowed no more than one run in a six-start stretch from Aug. 17-Sept. 14, becoming the only rookie besides Los Angeles' Fernando Valenzuela in 1981 to build such a streak in the last 50 seasons. Cain also flirted with no-hitters on multiple occasions. Besides his Oakland gem, Cain no-hit the Los Angeles Angels for 7 2/3 innings on June 19 before finishing with an eight-inning one-hitter, threw one-hitters lasting 5 2/3 and seven innings and fashioned a two-hitter over eight innings for his final victory Sept. 14 against Colorado.

"That's going to come sooner or later, hopefully," said Cain, appearing intrigued by the possibility of achieving a no-hit milestone. "You want to be able to do that once."

Cain also possesses an aptitude that has hastened his improvement. When he's presented with something new, said Giants pitching coach Dave Righetti, "you don't have to tell him twice."

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Thus, when Cain answers a question about how his perspective has changed now that he's in his third big-league camp, his well-worn response sounds more genuine than hackneyed. He truly understands the pitfalls of complacency, although the notion that he won't make the season-opening rotation is ludicrous.

"I have to compete like usual," said Cain, who finished 13-12 with a 4.15 ERA last season and tied for fifth in the National League Rookie of the Year balloting. "There are always guys coming in here kicking to come up. I feel like I always have to perform to earn my spot."

After all, Cain was among those ambitious prospects not long ago.

"You've got guys who want to come up as badly as you did at that time," he said.

One of them is Tim Lincecum, the Giants' top pick in last June's First-Year Player Draft who's in camp as a non-roster invitee. Righetti noted with amusement that Cain bemoaned Lincecum's overeagerness after watching him throw too enthusiastically in a game of catch: "He won't do that again," Cain said, as Righetti related.

It's also worth pointing out that Lincecum, regaded as The Next Big Thing in Giants camp, is 3 1/2 months older than Cain. Clearly, the dew is still moist on Cain's career.