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MESA, Ariz – The open battle in the A’s starting rotation is enough to fill manager Bob Melvin’s agenda, but Oakland also has competition to sort out in its bullpen.

Five relievers appear locked into spots even with closer Sean Doolittle sidelined with a shoulder injury – Fernando Abad, Tyler Clippard, Ryan Cook, Eric O’Flaherty and Dan Otero. If the A’s carry a seven-man bullpen as usual, that leaves two jobs open, and several candidates going for them.

R.J. Alvarez, a 23-year-old fireballer acquired from San Diego in the Derek Norris trade, is expected to get consideration based on his power stuff. Another newcomer, lefty Eury De La Rosa, was among those to throw off the mound Monday. De La Rosa, who turns 25 this week, was acquired from Arizona for cash in December. Melvin said he gleaned some insight from his former bench coach, Chip Hale, who got familiar with De La Rosa after being hired as the Diamondbacks skipper early in the offseason.

De La Rosa posted a 2.95 ERA in 25 appearances with the Diamondbacks last year and his career splits are fairly equal against lefties and righties.

“From watching him throw, it looks like there’s some funk and deception,” Melvin said. “He’s got a pretty good breaking ball. The numbers left on left (are solid), and he’s a guy who can get some righties out with his changeup too.”

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Melvin is more familiar with returners Fernando Rodriguez and Evan Scribner, and he’s spoken highly of the early work turned in by both this spring.

The A’s are without a key lefty in Doolittle, who has yet to start throwing as he recovers from a slight tear in his left rotator cuff. They’ll have to decide on a temporary closer until he returns. But even without Doolittle, the A’s still have two effective lefty relievers with Abad and O’Flaherty. Abad allowed just 13.2 percent of his inherited runners to score last season, the fourth lowest rate by an A’s reliever since 1974. O’Flaherty posted a 2.25 ERA in 21 games, and he said he expects to be sharper this season, his first full campaign since returning from Tommy John surgery.

A wild card in the bullpen equation will be left-hander Drew Pomeranz. He’s squarely in the race for a rotation spot, but if he’s not one of five starters, Melvin mentioned him as a candidate for the long relief role he held for part of 2014.

“I think it’s a luxury that we have O’Flaherty and Abad, two other lefties (besides Doolittle), and we’ll see how it plays out with Pomeranz. We could have a long lefty in there too,” Melvin said. “If Pomeranz is in the rotation with Doolittle out, that definitely factors in (to whether they need to keep a third lefty reliever). But we really are in a great position to have two left-handers that can pitch deep in games. And in the case of O’Flaherty, a history of getting righties out too.”

Alvarez, who has switched organizations twice in the past seven months, is worth keeping an eye on. He was dealt from the Angels to the Padres in the deal that sent Huston Street to Anaheim. San Diego called him up in September for his big league debut, and Alvarez limited opponents to a .115 batting average, though he did issue five walks in 8.0 innings. The right-hander touches the high 90’s with his fastball and his slider has shown flashes of being very good too, but obviously command is the issue.

“It’s fun, me being so young and being talked about for the bullpen,” Alvarez said. “ A lot of these guys are really good, and a lot of them have had great careers so far. It’s fun to go out there and show what you can do.”