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3/6/2014 7:45 P.M. ET

Cook's optimism transforms into confidence

PHOENIX -- After Ryan Cook threw his first bullpen of the spring on Thursday morning, his confidence level was off the charts.

Oakland's right-handed reliever, no longer nursing shoulder inflammation that sidelined him in late January, was already pretty certain he would be ready by Opening Day. Now, 20 pain-free pitches off a mound later, he has no doubt in his mind.

"I'm way more confident," said Cook, who made 71 appearances for the A's in each of the last two seasons. "That's like a double-edge sword, because I felt confident the whole time. To say I'm more confident is strictly because I felt good, not because I was doubting myself.

"Everything felt great, really good. Pleasantly surprised isn't the right term to use, because I'm not surprised, but I would say instead of optimistic, I'm confident. I don't want to say I didn't expect it to feel that good, but I was happy it did."

Cook limited his pitches to fastballs, but he said he had already been working on his offspeed pitches in flat ground sessions. He will most likely throw another bullpen this weekend and, barring any setbacks, face hitters in live batting practice next week in advance of his Cactus League debut.

"You start to feel like, wow, I can speed the process up and get in a game shortly," he said, "as opposed to, you're so far away and you see other guys get out there and compete and you really start to miss the competition factor of it all.

"I competed with myself a little bit today. I didn't try to blow anything out or try to go 100 percent effort-wise. I just tried to make pitches as if I was facing a hitter."

Cook still has a chance to appear in at least five or six exhibition games, a total the A's believe is enough to deem him ready for Opening Day. Asked if it was important to have two of those appearances come on back-to-back days, the 26-year-old responded, "I don't think that's really an issue."

"Especially with the strength of our bullpen," Cook said. "I think that I can get through the first little bit without having to do that. We talk about it all the time. I think our bullpen is really good."

Callaspo may debut at first base vs. Arizona

SCOTTSDALE, Ariz. -- Friday has the makings of a big day in A's camp. Not only is lefty Scott Kazmir slated to finally make his first spring start, but Alberto Callaspo is penciled in to make his debut at first base.

Callaspo has played five different positions in the Majors, but never first base -- not even in a Spring Training game. The A's believe he has what it takes to form a nice little platoon with Brandon Moss, though.

"As far as the skill-set goes," manager Bob Melvin said this week, "there's no reason he shouldn't be able to be a very good first baseman."

Melvin said Callaspo had "a little back issue" Thursday, which could postpone his first base debut. Melvin said he would wait until Friday morning to decide if the problem was serious enough to warrant scratching Callaspo from the lineup.

"That would be the only thing that would affect him," he said.

Gray struggles to get ahead vs. D-backs

SCOTTSDALE, Ariz. -- Sonny Gray was targeted for 45 pitches on Thursday, but the A's righty needed 35 of them in the first inning, and that's all the action he would see against the D-backs.

Gray struggled to get ahead of almost all eight of his batters, with five collecting hits and four scoring runs in his second spring start.

"It's tough getting hit around like that, but coming out of the game I felt really good," Gray said, "and my body and arm feel really good."

"They hit some fastballs up, out over the plate off him," manager Bob Melvin said. "He's going to have some outings like that. We don't really worry about him. Just threw a lot of fastballs today."

And changeups. Gray's curveball, meanwhile, was used just once on the day.

"As good as my changeup was last week, it was up and got hit pretty hard today," Gray said. "It's just something that's going to take a little more work. Maybe next week I'm going to just get back to pitching and trying to get guys out, whether it's throwing more breaking balls or what not.

"It all comes down to getting ahead of guys, and I just didn't do that."

A's in no hurry to rush Gentry back to field

SCOTTSDALE, Ariz. -- Craig Gentry is "very close" to returning to the field, manager Bob Melvin said, but there is still no timetable to get the A's outfielder in a Cactus League game.

Gentry has been sidelined by a lower back strain for two weeks, leaving the former Ranger unable to do much of anything in front of his new team.

"Once we get him out on a field, we'll see how many at-bats we can get him," Melvin said. "To an extent, a lot of it has to do with how he feels, first physically, and then at the plate. We want to make sure that we feel comfortable progressing him into a certain amount of games, a certain amount of innings.

"He feels great. He wants to get out there, but there's a progression that we need to see."

Despite Gentry's setback, Melvin still seemed confident he would be good to go by Opening Day, saying the club was being "overly cautious" in an effort to avoid a relapse.

In the meantime, Sam Fuld and Michael Taylor -- next in line behind Gentry on Oakland's outfield depth chart -- have been seeing plenty of playing time. Taylor has five hits in his last seven at-bats. Fuld hit his first homer of the spring on Thursday and is sporting a .333 average through seven games.

"We knew that he was this type of player, and he was a guy we were happy about getting when we did," Melvin said Thursday of Fuld. "When you have him as depth, with the Gentry situation right now, you're in a pretty good situation.

"He's a big league player. We can only have 25 guys, and we'll see what 25 guys we start with."

Worth noting

• Lefty Sean Doolittle remained perfect this spring, throwing his third consecutive scoreless inning in Thursday's game. He is yet to give up a hit or a walk and has five strikeouts in three appearances.

Closer Jim Johnson also pitched in Thursday's game against the host D-backs, allowing a run on one hit and one walk in an inning of work.

• With two hits on Thursday, including his first home run of the spring, Brandon Moss has reached base safely via hit or walk in each of his four games, three of them of the multi-hit variety.

Josh Reddick went 1-for-3 on Thursday with his third double of the spring.

Jane Lee is a reporter for MLB.com. Read her blog, Major Lee-ague, and follow her on Twitter @JaneMLB. This story was not subject to the approval of Major League Baseball or its clubs.