Nationals starting pitcher Edwin Jackson delivers during the first inning of Sunday’s third straight loss to the Yankees. (Alex Brandon/Associated Press)

Since the start of the season, the Washington Nationals have spent more time than not atop the National League East standings, unfamiliar territory for a franchise with a bleak history and a team built on youth.

The Nationals are on a 96-win pace with the third-youngest roster in baseball, one that has little experience in high-pressure games. Having played seven straight series against teams with .500 records or better, the Nationals will begin yet another Tuesday against a 2011 playoff team, the Tampa Bay Rays, before they face the Baltimore Orioles, a surprising contender.

With an average age just under 28, the Nationals are older than only the Kansas City Royals and Houston Astros. Their leadoff hitter is a 23-year-old rookie with 180 career at-bats. Their star outfielder is 19, still learning how to deal with disappointment. Their best three starting pitchers are 26 or younger. Of the 25 players on the active roster, only six have postseason experience.

In contrast to their young team, their manager is experienced. Davey Johnson, who has managed over 2,100 games, won the World Series in 1986 and made the playoffs five times. He said the Nationals’ rough weekend, in which they were swept in three games by the Yankees, could become an important step — particularly because it happened before a combined crowd of 124,135, only the second time in Nationals Park history that all three games of a series drew more than 41,000 fans.

“It was a great experience for the ballclub,” Johnson said. “Full house, playing the Yankees. I mean, that’s a good way to get a quick education.”

Four years ago, starter Edwin Jackson, one of four Nationals players on the 40-man roster to have earned a World Series ring, was on a young team that unexpectedly rocketed into the spotlight with a 2008 World Series appearance. Those Tampa Bay Rays had plenty of potential but were the worst team in the American League the previous season.

After an early winning streak, the players realized they could compete. Then it just kept happening, aided by two brawls along the way, one a famous fracas in Boston in June, that Jackson said “set the tone that we weren’t going to be pushovers.

“From then on, we just continued with the cockiness that we could win any ball game regardless of the pitcher on there,” he added.

Jackson said he already sees that confidence in the Nationals’ clubhouse. “Once you take that field with that mentality, you’ll play like it,” he said.

The Nationals have stayed in first place thanks to their strong pitching and depth, and despite a rash of injuries that has put 14 players on the disabled list. They also have lacked consistent offensive production from their middle-of-the-order hitters, Michael Morse and Ryan Zimmerman. But to stay in contention, they surely will need more than three combined home runs and 26 runs batted in from their third and fourth hitters.

The team has leaned on younger players such as Ian Desmond, Steve Lombardozzi and 19-year old Bryce Harper to spark the offense. But they, too, are learning to deal with success and the pressure that accompanies it.

Following the worst performance of his professional baseball career Saturday, an 0-for-7 day with five strikeouts, Harper was shaken. He had slammed his bat down after one at-bat, jawed with the home plate umpire twice and declined to talk about it afterward with reporters.

That’s when veteran first baseman Adam LaRoche, the team’s best hitter so far, saw an opening and stepped in. As the Nationals struggled to score runs in a key game, Harper hacked and kept missing, trying to do it all himself. LaRoche grabbed the rookie and told him to keep his head up and to shake it off. This is all normal, he told him.

“You lose a couple games early as a youngster, it can feel like the end of the world,” LaRoche said. “I’ve been there. It was there when I was a rookie, first couple years. It was like, ‘Oh, shoot, we gotta do something.’ In the scheme of things, it’s going to happen. We’re going to have way worse stretches than losing two or threes game, I’m sure.”

The best response comes from “guys that can stay the course and not stress over it, keep loose and go have fun and play,” he said. “Those streaks tend to not last as long with a group of guys doing that.”