PHOENIX — Mike Piazza appears perfectly comfortable with his new gig, even if he’s really not.

He smiled Thursday as he made his way onto the field minus catching gear for the first time in his career, the last member of the Oakland Athletics to get outside for stretching as he embarked on becoming a full-time designated hitter.

At 38, Piazza is ready to begin a new baseball life. The A’s don’t want him to catch at all to ensure that he stays healthy — and manager Bob Geren asked him to take it easy in drills Thursday.

Piazza stood in the back of the group once he was on the field, doing some warming up on his own before the A’s got going because he couldn’t stay still on Day 1.

After 15 seasons as a catcher, he will be playing in the American League and as a regular DH for the first time, hitting cleanup for the defending AL West champions. His arrival at Oakland’s Papago Park complex drew a Barry Bonds-like media crowd along with a large group of fans.

“It was weird not blocking balls for the first time, but it’s been fun so far,” Piazza said. “I know what I’m here for but I know it’s going to be very difficult for me to put the gear on the shelf and just hit. I’m an old catcher at heart.”

Piazza still might pull on his catcher’s mask at some point this spring to help out with pitchers throwing bullpens, though the A’s want him to focus his energy on hitting. Geren hopes Piazza, Oakland’s No. 3 backstop, won’t catch a game this year. But he’ll sit in on pitcher-catcher meetings to “bring his expertise in the mental side,” Geren said.

If starter Jason Kendall or backup Adam Melhuse were to get hurt, the A’s plan to bring up another catcher from Triple-A Sacramento rather than throwing Piazza into the mix.

Piazza, who became a first-time father to a baby girl, Nicoletta, on Feb. 3, is trying to accept that.

“I’m not going to shelve it completely but I do have to be careful and realize what I’m here for,” he said. “Slowly, I’ll get in there. Catching’s really the only way I know how to get in shape as far as getting ready to play.”

He has long admired Edgar Martinez and Frank Thomas for their abilities to contribute with only their bats.

It’s the Big Hurt who Piazza is replacing. Thomas led the A’s with 39 home runs and 114 RBIs in 137 games in 2006, remaking himself with Oakland after two injury-shortened seasons with the Chicago White Sox. He homered twice in Game 1 of a division-series sweep of Minnesota last October — his first postseason homers since 1993 — and also had a hit in both Games 2 and 3 to finish the first round at .500 (5-for-10).

“It’s too much pressure,” Piazza joked about needing to produce even more.

“I’m just as curious as anybody. ... Obviously, Frank set an incredibly high bar here last year at the DH position. I really think it would be foolish of me to try to measure up to that. I feel like I have to be the hitter I am.”

After leaving the New York Mets as a free agent, Piazza was thrilled to get a new start with San Diego last season. Then, in December, he received an $8.5 million, one-year contract from the A’s.

While Thomas had 556 plate appearances last season to only 439 by Piazza, A’s general manager Billy Beane is convinced Piazza will build on that number.

“We knew if we lost Frank that Mike was a natural segue for us,” Beane said. “Immediately when we talked to Mike, we made it clear what we wanted him for, and at this point in his career it was something he would embrace.”

His new teammates are embracing it, too, even those who were big fans of the Big Hurt. The A’s are always appreciative of how Beane is able to add key pieces and keep a winning product on the field even after losing big names.

“It’s cool,” third baseman Eric Chavez said. “(David) Justice, Ron Gant, every year it’s some veteran, savvy, good clubhouse guy. I’m sure Mike will be no different. I’m not going to lie, I’m sad to see Frank go. Frank was unbelievable last year as a positive influence.”

Piazza, who has a strong chance to become a first-ballot Hall of Famer, batted .283 with 22 home runs and 68 RBIs in 126 games for the Padres after nearly eight years with the Mets. Piazza also played for the Los Angeles Dodgers and Florida Marlins.

“I expect him to be the Hall of Fame hitter he is, a right-handed force in our lineup,” Geren said. “I expect him to feel better and play more games than he did last year as a DH. He is a tremendous guy who wants to help any way he can.”