They sit centrally in the Orioles clubhouse at Ed Smith Stadium.

Jeremy Guthrie has the first locker in the row and the closest path to the shower. Brad Bergesen dresses two stalls down, and next to him is fellow second-year pitcher Chris Tillman. Tillman's locker mate is Kevin Millwood, 14 years his senior. Millwood's neighbor to the right is the left-handed Brian Matusz, who was in elementary school when the veteran made his big league debut.

Normally at this early juncture of spring training, the Orioles' starting staff is cloaked with uncertainty, a mixture of untested youngsters and flawed veterans battling to fill the back end of the rotation. This year, the five pitchers expected to occupy the Orioles' Opening Day rotation are front and center, for everybody to see.

"It's definitely defined," pitching coach Rick Kranitz said. "I'm excited about it. You look at that rotation, that pitching staff, and those guys know where they are and who they're fighting with for a spot. That's the way it's supposed to be."

Publicly, Kranitz and manager Dave Trembley say the fifth spot in the rotation is up for grabs -- that Tillman must beat out David Hernandez and Jason Berken, who combined to make 43 starts in their rookie seasons in 2009. But it is widely believed that Tillman, a 21-year-old right-hander who went 2-5 with a 5.40 ERA in 12 starts last year, would have to falter badly this spring to not join Millwood, Guthrie, Bergesen and Matusz in the rotation.

"I've had the mentality that I'm going to have to go and earn it," Tillman said. "I went into the offseason thinking that, and I went into spring training thinking that."

At this time last spring, the Orioles' rotation consisted of Guthrie and right-hander Koji Uehara. Twelve other pitchers waged a competition for the other three spots, which eventually were won by Alfredo Simon, Mark Hendrickson and Adam Eaton. That was despite the fact that Simon was the only one of the three to have a strong spring.

The number of pitchers involved in the competition made it difficult for Trembley and Kranitz to get their starters the required spring workload. "You look at the guys that were starters for us last year and they didn't get many innings in the spring," Trembley said. "If you don't build the guys up in spring training, how can you expect them to go deep into games when the season starts? It can't be just one or two times. They have to break camp with innings on their belt, and they have to get to that 100-pitch plateau in spring training."

Kranitz said he likes to get his starters between 22 and 25 innings in the Grapefruit League. Because of Guthrie's stint with Team USA in the World Baseball Classic, Uehara's balky hamstring and so many auditions for the other rotation spots, no Oriole reached that mark last spring.

"It was always like, 'OK, now who do we try next?' " Kranitz said. "The last two years have been real hard in that sense. Now, it's, 'Here it is.' It makes a lot of difference. You can set up the bullpen how you want it, you can set up your rotation how you want it. Once you decide on one through three or four, you can start slotting them in like it's the regular season."

Several of the pitchers also said the current situation gives the group time to develop camaraderie, a process Guthrie said has already begun. Millwood, acquired in December from the Texas Rangers for his ability to provide quality innings and leadership, spoke at length to Bergesen as both sat near their lockers Thursday. Guthrie, Matusz and Tillman have been close since last spring. Tillman said the potential rotation members already have discussed a group fishing or golfing outing.

It's an interesting mix of personalities. Millwood is as laid-back as Guthrie is hyper. Bergesen generally keeps to himself, while Tillman and Matusz are together constantly -- talking, scheming and doing what normal twentysomethings do. Their pitching styles vary greatly as well. "[In Matusz], you have a lefty power pitcher with great stuff and a tremendous head on his shoulders.," said Guthrie, who had a difficult 2009 season, going 10-17 with a 5.04 ERA but logging 200 innings. "You have a tremendous sinker-ball pitcher [in Bergesen] that is consistent in the zone. And then you got guys that try to use a mixture of pitches. I think it's a great mix."

The club is likely at least a year away from being able to call starting pitching one of its strengths. But the potential is certainly there for this to be one of the better staffs the Orioles have had in awhile.

Millwood, 35, went 13-10 with a 3.67 ERA as the veteran anchor of a young Rangers staff last season. Orioles officials are confident that Guthrie, 30, will return to the form he showed in 2007 and 2008, when he posted sub-4.00 ERAs.

Bergesen, 24, was 7-5 with a 3.43 ERA in 19 starts last year before he was hit in the left shin by a come-backer that ended his season. He hurt his shoulder in December, but he is on track to be ready for the season.

Matusz, 23, went 5-2 with a 4.63 ERA in eight starts last season and will be a popular preseason pick for the American League Rookie of the Year award. Though Tillman struggled to find consistency in his dozen starts last year, scouts believe that he has more upside than any other pitcher in the Orioles organization.

And if any of those five are injured or struggle, Hernandez, Berken or prospect Jake Arrieta will be available to take their place. Trembley said last week that Uehara will compete only for a bullpen role this spring.

"We have options, and we have flexibility," Trembley said. "I think it says a lot for the development of our younger players. We have more good choices for fewer slots. To me, that's really important."

Opening Day rotations
A year after going to spring training with three undecided spots in the rotation, the Orioles' starting staff is essentially set with veterans Kevin Millwood and Jeremy Guthrie and youngsters Brad Bergesen, Brian Matusz and Chris Tillman.
Here is a look at the Orioles' Opening Day rotations the past five seasons:
2009: Jeremy Guthrie, Koji Uehara, Alfredo Simon, Mark Hendrickson, Adam Eaton
2008: Jeremy Guthrie, Daniel Cabrera, Steve Trachsel, Adam Loewen, Brian Burres
2007: Erik Bedard, Daniel Cabrera, Jaret Wright, Adam Loewen, Steve Trachsel
2006: Rodrigo Lopez, Erik Bedard, Kris Benson, Daniel Cabrera, Bruce Chen
2005: Rodrigo Lopez, Daniel Cabrera, Erik Bedard, Sidney Ponson, Bruce Chen