Manny Acta confirmed as much Saturday when the manager named right-handers Shairon Martis and Jordan Zimmermann his Nos. 4 and 5 starters, finalizing an Opening Day rotation that will include three homegrown products of Washington's farm system.

"What makes it more exciting is that they're young guys under 25 years old from our system," Acta said. "We didn't have to run a tryout camp out there like we did the last two years."

Indeed, the days when a dozen pitchers with names like Jerome Williams, Mike Bacsik and Jason Simontacchi engaged in a spring-training battle royal for rotation spots are over. The pitcher Martis and Zimmermann beat out this spring was a 22-year-old Collin Balester, a top prospect himself who remains in the organization's long-term plans.

The 21-year-old Martis, who pitched in five games with the Nationals last September, and Zimmermann, who will make his big league debut April 19 against the Florida Marlins, join John Lannan (24), Scott Olsen (25) and Daniel Cabrera (27) in a rotation that is short on experience but high on potential.

"You're going to have a lot of ups and downs with young pitchers," said Olsen, who started between 31 and 33 games each of the past three seasons with the Marlins. "I had them, I'm still having them. ... It

just kind of comes with the territory of being a young pitcher and making the adjustments"

The Nationals felt it was worth the risk with Martis and the 22-year-old Zimmermann because each pitches with the poise of a seasoned veteran. It didn't hurt that each has dominated on the mound this spring.

Martis has a 1.42 ERA in five appearances, holding opposing hitters to a .154 average. Zimmermann wasn't scored upon until his fifth outing and has struck out 20 while walking only two.

"Nobody won it by default. They both earned the spot," acting general manager Mike Rizzo said. "You've seen these guys pitch. They not only could pitch at the back end of our rotation. They could pitch in just about anybody's rotation that I've seen down here in Florida."

Martis didn't garner much attention during the offseason and early spring. The Nationals' front office and coaching staffs, though, have been high on the unassuming right-hander for a while and saw him as a viable rotation candidate from the first day of camp.

Martis' best move might have been his decision not to pitch for the Netherlands in the World Baseball Classic. By remaining in Washington's camp, he was able to get more innings and make a firsthand impression on those who ultimately decided his fate.

Martis also believes his big league experience last fall helped ease his comfort level this spring.

"I know more about the league," he said. "Things that I was working on last year, I came in better in those things. That gives me more confidence to play on this team."

Zimmermann, a second-round draft pick in 2007 from Wisconsin-Stevens Point, received all kinds of accolades during the offseason as Washington's top-rated prospect. He came to camp thinking he had a shot to make the roster but said he didn't expect his rise to be so quick when he was first drafted.

"I thought maybe it would be three or four years and I'd try to get maybe close to the big leagues," he said. "For it to come this fast, it's kind of overwhelming."

Zimmermann won't be on the Nationals' Opening Day roster. Because of scheduled off days, the club doesn't need a fifth starter until April 19, so he'll open his season either at Class AAA Syracuse or perhaps a warmer site depending on weather conditions.

Team officials insisted the decision to start Zimmermann in the minors had nothing to do with keeping his arbitration clock from starting, and Acta said he wished his team didn't have any off days to open the season so Zimmermann could be in the big leagues from Day One.

"I think it's better for me to be up there when I'm ready to go," he said. "And obviously I'm not ready to go right now. I'm just going to go down there and work hard and show them I am ready to come back up."