WASHINGTON – When manager Dave Martinez walked into the Nationals’ clubhouse this weekend, nine players on the 26-man roster were 25 or younger, including four born in the year 2000.

“I’m feeling old,” Martinez said with a laugh.

Sunday exemplified the youth movement. On the day 23-year-old shortstop CJ Abrams was named to the All-Star Game, rookie left-hander DJ Herz (No. 12 prospect) took the mound with rookies James Wood (No. 1 prospect, MLB No. 2 overall) in left field, Jacob Young in center field and Trey Lipscomb at third base were in the starting lineup.

“We worked really hard in our organization to get to this point,” Martinez said. “We started this so-called rebuild knowing that these players would eventually get up there. Now, you’re starting to see them all get up here and play and really make an impact on the game.”

The Nationals’ 8-3 loss to the Cardinals on Sunday had instances that showed the team's youth and inexperience. These in-game moments will become talking points and topics of emphasis as they encounter learning curves.

“The vibe is good,” said Herz. “... I guess for all of us, it’s just going to be experience -- and that’s something that you’ve just got to take your time and learn. These guys are all talented. It’s a lot of fun to see, especially when it all clicks together.”

This homestand has been highlighted by the Major League debut of Wood. This week alone, the 6-foot-7 21-year-old collected his first home run, double, multi-hit game, multi-RBI game, walk and stolen base. Wood is batting .320, and he has reached base safely in his first seven games, the second-longest streak by a Nationals rookie in team history (2005-present).

“You saw some of our young players hit home runs yesterday, drive in a bunch of runs,” said Martinez. “That’s rewarding, not only to me, but I know [it is to] everybody in this organization because we’ve all put a lot of time into trying to prepare these guys to get up here to the big leagues.”

In order to make room on the 40-man roster for Wood, veteran outfielder Eddie Rosario (.183 batting average in 67 games) was designated for assignment on Monday. Six days later, veteran third baseman Nick Senzel also was DFA’d after batting .209 in 64 games. In a corresponding move, Lipscomb was called up from Triple-A for his fourth Major League stint this season.

Lipscomb and Wood are two of five prospects (along with infielder Nasim Nuñez and southpaws Mitchell Parker and Herz) to have made their big league debuts with the Nats this season. They joined a 25-and-under group of catcher Keibert Ruiz, left-hander MacKenzie Gore, second baseman Luis García Jr., and Abrams.

“It’s been fun watching these guys play and watching their growth -- and they keep coming,” said Martinez prior to Sunday's contest. “There’s a lot more work to be done. I’m looking forward to today’s game, but beyond that, the future of our organization because we’ve got some really good players.”

With every Major League callup, the development continues on the Minor League level. Third baseman Brady House, ranked as the Nationals’ No. 3 prospect and MLB No. 44, was promoted from Double-A to Triple-A on Sunday.

“What I learned about him [in Spring Training] is that he’s a really good third baseman, he really is, and he loves to play the game,” Martinez said.

In 75 games with Harrisburg, House slashed .234/.310/.423 with a .733 OPS, 11 doubles, 13 homers, 24 walks and five stolen bases. There will be an emphasis for the 21-year-old to hit the ball in the zone and accept his walks in Rochester, where he joins No. 2 prospect (No. 4 overall) Dylan Crews, 22.

“When you get to Triple-A, it’s about consistency,” said Martinez. “That’s going to help you up here in the Major Leagues. We’ll definitely keep an eye on him, we’ll have reports on him now every day and we’ll see where he’s at. But he’s there, he’s knocking on the door.

“He’s just another one of our young guys that we feel like can help us up here in the big leagues.”