PHOENIX -- Takashi Saito's calf injury threw a bit of a wrench into the D-backs' roster plans, as the righty reliever was placed on the 15-day disabled list Wednesday.

An MRI Wednesday morning revealed a right calf strain, and Saito won't be eligible to come off the DL until April 15. Manager Kirk Gibson announced lefty Wade Miley will assume Saito's roster spot, the lone remaining on Arizona's Opening Day roster.

For much of the spring, Gibson's bullpen appeared set. But Saito's injury, which he sustained while stretching before Tuesday's game, changed things.

It left Miley and lefty Mike Zagurski as the two remaining options. Zagurski has looked very impressive this spring, but Gibson said long relief can't be overlooked early in the season. That sealed the job as Miley's, given his background as a starter.

"Right now your starters aren't stretched out as much, so you tend to rely more on your bullpen," Gibson said. "I would rather do that then push the [starters] early in the season."

Zagurski was outrighted to Triple-A Reno, meaning he cleared waivers. The D-backs acquired Zagurski from Philadelphia last September, and he was out of options this spring.

Zagurski finished Spring Training with a 2.61 ERA, while opposing hitters hit just .189 against him. His stats were better than Miley's (5.59 ERA) but Miley seemed to fit what Gibson was searching for a little better.

Gibson pointed to Joe Paterson as his matchup lefty and said Craig Breslow would be his second option for left-handed hitters -- a guy who could go an inning, and at most two. That left room for Miley to fill in as the club's long man because Gibson didn't feel comfortable stretching out Breslow or Bryan Shaw.

"If you don't have a guy that can pitch 4-5 innings, then you blow your bullpen out for days," Gibson said.

That said, it's likely Gibson will be more comfortable in two weeks without a long man because his starters will be stretched out further and working deeper into games. That would seem to put Miley in position to return to the Reno starting rotation when Saito is healthy.

Gibson: Rotation remains unchanged

PHOENIX -- For the entire second half of the spring, manager Kirk Gibson has reiterated that the D-backs rotation is set and Josh Collmenter will start the club's third regular-season game.

But by keeping Patrick Corbin on the roster until Tuesday, many speculated that the young lefty could be poised to take Collmenter's spot, had the right-hander faltered in his final outing.

Collmenter didn't, tossing three hitless innings Tuesday against the Brewers, and afterward Gibson brushed aside talk that there was a chance Collmenter's spot was in jeopardy. But Gibson acknowledged Corbin was in the hunt to make the team.

"He was in the hunt for a position on the team," Gibson said Wednesday morning. "I'm not going to go into all the details. There were a lot of discussions that take place, and you think about all the different scenarios and what any given scenario may do for your ballclub."

Gibson replied with a pointed "no" when asked if Collmenter's job was ever in question.

"I'm not going to get into that," he said. "The rotation's set, it was set a while ago."

As for Corbin, his 3.00 ERA and .178 opponent's batting average was enough to impress Gibson.

"Ultimately we decided to send him to Double-A, let him pitch every fifth day," Gibson said. "He's had an outstanding spring. He's learned a lot, he's hungry, and ultimately we decided that would be the best place for him to go."

Kennedy excited to take ball against Giants

PHOENIX -- Getting the ball on Opening Day is more than enough to get the adrenaline flowing for D-backs righty Ian Kennedy.

Getting the ball on Opening Day at home, against the division-rival Giants, whom the D-backs beat out last season to claim the National League West crown, only multiplies that adrenaline.

In his second straight Opening Day start, Kennedy knows the nerves will be there. He says the challenge will be to harness the excitement and find a comfort level on the mound.

"I feel like this year, since it's against the Giants at home, it's going to be a little bit more intense for our players," Kennedy said. "For myself, I'm going to try and keep it to a minimum."

For Kennedy, that means getting through the first inning. Once he does that, he says he'll be able to settle into a groove.

Kennedy is coming off a spring in which he posted a 3.98 ERA in five starts. He says any nerves he feels on the mound are no different than the emotions of every other pitcher in the league when they start their seasons.

"I think the first start for every pitcher every season is going to be a little more adrenaline, just because it's not Spring Training," Kennedy said. "You haven't pitched in an adrenaline-filled game in four or five months, and it's just a little different."

Kennedy said he'd call on his experience pitching in big games -- Opening Day 2011 and Games 1 and 5 of last year's NLDS -- to calm himself.

But he'll take some time to enjoy the feeling of pitching on one of the biggest stages in baseball, against arguably the biggest competition in the D-backs' attempt to repeat.

"That adds a little bit to it." Kennedy said of facing the Giants. "They're going to be excited, just like we are, and full of the Opening Day atmosphere. Like I said, the target's on our back, so it's going to be a lot of fun."