BOSTON – Just call them the Downeaster Quartet.

Last year, they were playing Double-A ball for the Portland Sea Dogs. This season, they’re up in the majors, not only playing for the Boston Red Sox, but making valuable contributions.

They are Jonathan Papelbon, Jon Lester, Manny Delcarmen and Craig Hansen, and they’ve made the trip from Portland to Boston as quickly as Amtrak’s Downeaster train service.

“As everyone in Portland is aware, there are a lot of failures and successes along the way, and we’re pleased that as of now, their development has led them to roles where they can have some success at Fenway Park,” said Red Sox general manager Theo Epstein.

They wear the four highest-numbered uniforms (56, 57, 58 and 62) hanging inside a locker in the Red Sox clubhouse and are also the last four players listed last on the roster, but they’re anything but an afterthought.

“It’s hard for young players to perform for a team like this, with everybody watching you and all the expectations and pressure, and it seems like they’ve got all that under control,” said Sox slugger David Ortiz. “They’ve been doing a great job.”

It’s not unusual for four rookies to get called up to a veteran-laden, division-leading major league team – in September, when team rosters can be expanded. But in July? In the middle of a pennant race?

That’s rare enough, but all four are performing successfully on a regular basis in clutch situations.

“We’re not rebuilding here,” Sox manager Terry Francona said. “We’re trying to win, so that makes it even more astounding what they’re doing and a very big compliment to our player development people.”

Delcarmen, Lester and Papelbon were teammates at Single-A Sarasota two years ago. Hansen was drafted last year.

One could argue this is one of the most significant rookie impacts since 1975, when Fred Lynn and Jim Rice led the Sox to the World Series and Lynn was named both American League Rookie of the Year and Most Valuable Player.

“Usually, it happens one or two at a time, but this is a big wave of talent and I think it says a lot about our player development operation, our player development personnel and our affiliates and their ability to develop this talent to where it all comes together at once,” Epstein said.

Papelbon, selected to the all-star team as a rookie, leads this rookie wave with a major league-leading 29 saves in 32 opportunities. He’s the heavy favorite to win the A.L. Rookie of the Year award and is a solid Cy Young candidate as well.

“None of us are [surprised],” said Papelbon, 25. “I think we all expected to be here contributing. We all just want to go out there and win and help contribute to a winning ballclub.”

And they all are.

*Papelbon went into Wednesday afternoon’s game with a miniscule 0.54 ERA. The dominating righthander has 50 strikeouts in 50 innings while allowing 27 hits and nine walks.

“Pap’s got great stuff with really good location on his heater. He also has an outstanding split and good slider,” said Sox team captain Jason Varitek, who has caught the most games behind the plate in team history with 991.

*Lester pitched his longest game in the majors Tuesday night, allowing one hit over eight innings, and became the first Red Sox rookie lefthander, starter or reliever, to win his first five major-league decisions. Righty Aaron Sele is the only other Sox rookie to start off with five straight wins.

“We’re very happy with Jon Lester. It’s very hard to find what he brings to the table for us,” Epstein said. “I like his physical attributes, his delivery, his arm action, his stuff. I also like his composure. He’s not afraid to throw big pitches in big spots.

“I think the guy has a chance to dominate up here when it all comes together.”

*Delcarmen is 1-0 with a 3.25 ERA in 27 2/3 innings over 25 games. The 24-year-old righty has allowed just one run and struck out 12 batters in his last 10 outings (11 2/3 innings).

“Manny throws 95 [mph] with very good life on his fastball and he has a curveball that he can now count on to use along with his changeup,” said Varitek.

*Hansen is 1-0 with a 4.20 ERA. The first Red Sox player to reach the majors in the year he was drafted has allowed six earned runs over 14 1/3 innings in 13 games since being recalled from Triple-A Pawtucket on June 20. The righty reliever has also retired 12 of his 14 first batters this season.

“Hansen’s been a sinker pitcher, but we’ve added a four-seamer and he’s utilizing both sides of the plates more than last year with his slider and his changeup keeps getting better,” said Varitek.

Veteran influence

The four rookies credit the clubhouse atmosphere fostered by Boston’s veteran players for helping them feel at home almost right from the start.

“There’s a good comfort zone we have now where you can pretty much go to anyone in the clubhouse and ask them for advice or whatever,” said Hansen, 22. “When I first got here last year, there were definitely nerves going on with me, but guys like Mike Timlin took me under his wing and helped me a lot with the mental part of the game.”

That’s music to the ears of “Big Papi.”

“You want to give the guys the confidence and make them feel like this is where they belong – where they really belong – and make them feel this is where they want to be,” Ortiz said. “We want to let them know that it don’t matter how long we will be playing this game in the big leagues, we’ve got their back.”

And the rookies know it.

“It’s been a blast from the beginning. The guys on this team are unbelievable,” Lester said. “Having guys like Papelbon, Manny and Hansen here makes it so much easier, knowing you have guys you can go talk to and who always have your back.

“The veteran guys actually make it better for us more than those guys because they treat us so well here.”

Francona says the rookies themselves have a lot to do with the ease at which they’ve become part of this A.L. East division-leading team.

“When these kids get here and right off the bat help you win games, it’s because they know how to act,” he said. “They act professional and blend in, which is important when you have a veteran team.”

Four-shadowing

With a combined average age of 221/2 years for this foursome, coaches and team officials alike know success can be as fleeting as it is sudden.

“It’s still a work in progress, but the more experience they gain with the hitters and themselves, the better they’re going to be,” Varitek said.

That fact apparently is not lost on these rookies.

“I knew I could perform at this level and right now things are going well, but the season is long,” said Lester, 22. “You have to take the good with the bad and go from there.”

Francona likes the mindset of these players who act older than their years.

“It’s an ongoing story that’s not finished, but I think it’s a pretty nice success story because they’re carrying a big load for us and I’ve got no problem with that,” he said.

This foursome has not only made its presence felt on the field, but also in terms of people’s perceptions.

“It’s the first time we’ve been able to do that in the nine years I’ve been here is to reach within to give us some help instead of trading for it, and that’s a good thing,” said Varitek.

Whatever their future holds, one thing is certain: They will play a big part in the future of the Red Sox this season.

“Those young guys are not only a big piece of our future, they fit so well they’re a big piece of our present, too,” said Epstein. “I don’t know where we’d be without these guys. They’ve really stabilized our pen.”

“They’ve always had great stuff, but now they’ve really refined their whole package to where we rely on them in big spots in a game. They’re going to decide whether we win a lot of these games down the stretch.”