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3/26/2013 8:35 P.M. ET

Anderson ready to get season under way

GOODYEAR, Ariz. -- Brett Anderson's ready to leave the desert.

The A's lefty found that his breaking ball was "kind of non-existent" in his final exhibition start against the Indians on Tuesday, and he's thinking that it will be right back to form once throwing in air that isn't so dry again.

Good thing his next start is in Oakland, where he'll take the mound against the Mariners on Opening Night in six days.

"I'm ready to get back to the Bay," Anderson said. "It'll be good to get some humidity because it's always tough to spin stuff here with the thin air. But I like the way my arm feels. It'll be good to get in games that matter."

Anderson, who gave up two earned runs in 5 1/3 innings Tuesday, finished his spring campaign with an unofficial 6.75 ERA, a number that doesn't include his start in the Minor Leagues or the one he made against Team Italy. Nor is it one he, or his manager, really cares about. It's Spring Training, after all.

Anderson's next outing is of greater magnitude not only for the obvious reasons, but because it also happens to be his first career Opening Day nod. It will mark the eighth different Opening Day starter for the A's in the last eight years.

"I'm sure it'll kind of hit me as we get closer and closer, but obviously it's an honor to be the guy to go out there and lead your team in that first game," he said. "I'm excited for the crowd. Hopefully, it's the way it was in the playoffs last year, all rowdy. It'll be fun to be a part of."

Rosales to start season on disabled list

GOODYEAR, Ariz. -- With news of an injury to infield candidate Adam Rosales coming out Tuesday, the A's roster is suddenly taking shape.

The versatile Rosales, out of options and in good position to grab a roster spot, will instead open the season on the 15-day disabled list with a left intercostal strain. He may soon be joined by Hiroyuki Nakajima, who suffered a left hamstring strain Tuesday.

That leaves Jed Lowrie in charge of shortstop, with Scott Sizemore and Eric Sogard teaming up as a nice platoon at second base to commandeer Oakland's middle infield come Opening Day. It also leaves roster room for first baseman Nate Freiman.

The 29-year-old Rosales, injured in Monday's game while making a throw to home plate, was batting .324 with three home runs and nine RBIs in 21 games this spring. This marks the second time in three years he will begin the season on the DL, having sat out the start of 2011 while recovering from a fractured right foot.

"It's too bad, too, for a guy that's finally healthy again and putting together good at-bats and playing every position," manager Bob Melvin said. "It's a tough one to lose at this point, so hopefully he's healthy as soon as he can be and back in the swing of things."

The recovery time for intercostal strains varies, but typically players require at least a month off before returning to game action.

Nakajima sustains left hamstring strain

GOODYEAR, Ariz. -- Once bountiful in number, A's middle infielders are dropping like flies.

Oakland entered Tuesday with as many as six players vying for spots in the heart of the diamond and left it with only four of them healthy.

Just hours after announcing that Adam Rosales would start the season on the disabled list, the A's watched shortstop Hiroyuki Nakajima exit the 10th inning of a road game against the Indians with a left hamstring strain. He's considered day to day.

"It's too bad," manager Bob Melvin said. "Hopefully it's nothing significant and he'll be back playing in a few days, but you don't know with hamstrings. They can be difficult injuries."

Nakajima suffered the injury while running from first to second on a sacrifice bunt, just minutes after he had found his way out of a 0-for-20 slump with a base hit. He motioned for a trainer and walked off the field with a slight limp under his own power, ultimately deferring questions from the media before getting on the team bus.

The struggling infielder's murky health status only makes it that much more plausible that he doesn't begin the year on the A's 25-man roster. Rather, Jed Lowrie is likely to begin the season as the everyday shortstop, with Scott Sizemore and Eric Sogard sharing duties at second base. Andy Parrino, who is still in camp, is expected to start the year in Triple-A Sacramento.

That's where Nakajima seems destined to pick up more at-bats before making his Major League debut. Should his injury prove to be anything but minor, the A's could place him on the 15-day disabled list and have him rehab with the River Cats. Or, they can simply option him there before setting their roster.

Healthy or not, Nakajima still has work to do.

"He was working on some stuff in batting practice today, trying to use his back side and get his legs more involved," Melvin said. "He had a good BP today and took a good swing on that one there in the 10th, so maybe he's making progress, finding something that's working for him."

Worth noting

• Lefty Travis Blackley's struggles continued on Tuesday, when he was tagged with his second blown save of the spring after giving up two runs to the Indians in the ninth inning. He offered up another run in the 10th in an eventual 7-6 A's win.

Blackley has a 14.21 ERA spanning seven appearances, and he's quickly gone from a strong roster candidate to a player on the roster bubble. He's out of options, too.

"He's a guy we're trying to make a decision on, and those are the situations that you evaluate closely," Melvin said. "Neither inning were pitched very well. He'll tell you that."

Said Blackley: "I feel better than I have ever in my life. ... I can't wrap my head around why these runs are coming in."

• A's closer Grant Balfour, making just his third spring appearance Tuesday since coming back from knee surgery, tossed a perfect seventh inning.

• Third baseman Josh Donaldson has six hits in his last seven at-bats to raise his Cactus League average to .320.

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.