Mike Lowell receives high-fives after scoring the go-ahead run last night on a Jason Varitek single in the eighth inning.

The Providence Journal / Gretchen Ertl

BOSTON — The depth and development in which the Red Sox philosophy is based was on display last night at Fenway Park.

On the mound was 23-year-old rookie Justin Masterson making his seventh start of the season for Boston. At first base was 24-year-old Brandon Moss. In relief for Masterson was 27-year-old rookie Chris Smith.

All three have been recalled from the minors at various times this season for emergency purposes, and all three were needed big time last night.

In the end, however, the seasoned veterans proved crucial.

The Red Sox were trailing by two runs in the bottom of the eighth inning when Mike Lowell drilled a two-run double to tie the game before the struggling Jason Varitek drove in the eventual game-winner with a single to right to give Boston a 5-4 victory.

“The veterans took care of all the hard work,” said Smith, who earned his first major-league victory. “The young guys did all the easy stuff and the older guys took over and got the game under control.”

If it wasn’t for the gutsy six-inning performance by Masterson and the outstanding two-inning relief outing from Smith, the veterans may not have had an opportunity to capitalize.

“For us it means a lot,” Smith said. “We’re getting a lot of opportunities to come up and play. And, the guys who have gotten an opportunity have showed they can handle it up here and succeed. That shows all the players at Triple A and Double A that if you get an opportunity seize it and make the best of it.”

Because of the array of injuries to the Sox’ starting rotation this season, Masterson has been called upon and has been solid in the process. He entered last night’s game with a 4-1 record to go along with his 3.00 ERA. The young right-hander made one mistake last night when he surrendered a three-run homer to Arizona’s Chad Tracy in the third inning.

Masterson finished six innings and allowed a total of four runs on seven hits with four walks and four strikeouts.

“He’s done a terrific job,” said manager Terry Francona. “The kid comes up with just a few Triple-A starts under his belt and every time he pitches, he gives us a chance to win. He’s comfortable when he’s competing. He’s got a good routine to get ready to pitch. He’s polite and he wins more than he loses. It’s been fun to watch.”

Moss, who made his major-league debut at first base on Monday night, was back at the position again last night. Red Sox starting first baseman, Kevin Youkilis, suffered a right-eye contusion when he was hit in the face by a bad throw by Mike Lowell during warm-ups prior to the start of the fifth inning on Monday. Backup Sean Casey is serving his three-game suspension, so Moss became the man.

An outfielder by trade, Moss began working out at first base last fall for the Sox and has played 32 games at the position for the PawSox this season. There’s a simple reason why the Red Sox wanted him to play there.

“We felt like he has a major-league bat,” said Francona. “If he can play first base his value to the organization can be enhanced. He doesn’t have a lot of experience playing first; he’s still a little rough over there. But if he can handle it, all of a sudden you’ve got a pretty good left-handed bat that can do a lot of things. He could be pretty valuable.”

Last night, Moss was steady defensively and went 1-for-4 at the plate.

Smith, who made his major-league debut last Saturday and was very good in that four-inning outing, relieved Masterson to start the seventh inning and was outstanding in two scoreless innings. Smith didn’t allow a hit and walked only one to earn his first major-league victory.

“Chris Smith was beautiful,” said Masterson. “He was dirty. He was slicing and dicing and it was fun to watch.”

After the Red Sox scored four runs on six hits in the bottom of the eighth inning, Jonathan Papelbon redeemed himself for a blown save last Sunday — his fourth of the season — with his 22nd save of the season in the ninth inning.

It didn’t matter whether the Red Sox won or lost last night. It was just another example how successful their depth and development has become.

“It’s a testimony to the great scouting and great coaching throughout this organization, helping to develop guys to be able to help this be a dynasty,” Masterson said.

jmcdonal@projo.com