Who's the dark horse in spring training?

Dark horses, long shots, under-the-radar players, guys who come out of nowhere - every spring training, someone unexpectedly forces his way into 25-man roster consideration. Sometimes it's because of the kind of on-the-field performance that just can't be ignored. Other times, it's because an injury opens up an opportunity. Occasionally, a trade creates an opening. So who among those players soon to report to Space Coast Stadium in Viera, Fla., might fall into this category? Unlike previous springs, there are more sure things than opens spots up and down the Nationals' roster. That makes it more difficult for someone to come out of the blue. The Nationals didn't make a selection in the Rule 5 draft at the Winter Meetings, so they don't have to worry about finding a spot for someone who otherwise might be getting ticketed to the minor leagues. The pitching staff is packed - so much so that left-handers John Lannan or Ross Detwiler, or both, might be shuttled to the bullpen. There might not be room for right-hander Ryan Mattheus, who was 2-2 with a 2.81 ERA in 35 games as a rookie in 2011, though he lost time on the disabled list with a right shoulder injury. But manager Davey Johnson really likes Mattheus' competitive nature and make-up, which counts for something. Likewise, righty Yunesky Maya may be running out of opportunities, so this would be a perfect time for the 31-year-old Cuban enigma to pitch well enough to force the Nationals to make some tough decisions. Some in the organization think he's better suited for long relief than a starting assignment. If you want a long shot from the left side, consider Atahualpa Severino, who looked good during a late-season trial in 2011. The biggest question mark in the infield revolves around who will be the backup infielder. Veteran Mark DeRosa fills the need at the corner spots, assuming his surgically repaired wrist holds up, but who backs up in the middle? Homegrown Steve Lombardozzi has his backers on South Capitol Street, but there are also some in the organization who believe he needs more seasoning. Luckily for Lombardozzi, one of the guys in his corner is Johnson, so that may work to his benefit. But don't discount utility man Andres Blanco, in camp as a non-roster invitee. If Lombardozzi struggles, the Nationals could do worse than a switch-hitting veteran backup - think this year's version of Alex Cora - who doesn't really hit, but possesses a good glove, knows his role and understands how to stay ready. Phil Wood of MASNsports.com wrote about Blanco's chances at making the cut over the weekend. How the outfield stacks up depends on two main questions: Does Bryce Harper make the roster as the starting right fielder, or do the Nationals go with a platoon of Mike Cameron and Rick Ankiel in center? Roger Bernadina has been given chance after chance without fully seizing his opportunities and the Nats aren't sold on him - as a potential starter or as a long-term bench player. Could that open the door for someone else to make an impression? The Nationals used many of their 40-man roster spots to protect pitching depth and young players (Matt Purke, Tyler Moore, Anthony Rendon, Eury Perez). Of the outfielders in camp on non-roster invites, pay attention to veteran Jason Michaels and former perennial prospect Xavier Paul. At 35, MIchaels is a pro's pro who hits from the right side, comfortable in a backup role and able to play all three outfield position. Paul will be 26 later this month, boasts speed and versatility, and is still waiting for his power to develop. He's flamed out with the Dodgers and Pirates, but a new club gives him new hope.