BOSTON – After Justin Masterson finished his throwing session in the visiting bullpen Thursday at Fenway Park, the socializing began.

Masterson, 27, the ever-outgoing pitcher who used to light up Hadlock Field with his smile and sinking fastball, was a popular person Thursday afternoon, hours before the Indians-Red Sox game.

Masterson was not scheduled to start until today, so he had time to chat. And, for about 30 minutes, Masterson sat, talking, in the Red Sox bullpen.

It made you wonder.

What could the Red Sox have done if Masterson stayed in that pen, warming up as a starter or reliever? As a starter he pitches deep into games, effectively, and previously proved his worth out of the bullpen.

Portland Sea Dogs fans saw Masterson show his wares in 2007 and early in the 2008 season before he became a vital bullpen cog in Boston’s playoff run.

But the Red Sox decided, four months into the 2009 season, that they could get along without Masterson. He was traded in a deal that netted the services, albeit temporarily, of all-star catcher Victor Martinez.

It is a trend that Sea Dogs and Red Sox fans have witnessed every year. Players come through Hadlock Field as top prospects. Their future at Fenway is envisioned. And they may even get a taste of the majors in Boston.

In many cases, though, they are soon shipped out for more immediate help.

“I was called in a half-hour before I got traded,” Masterson remembered. “They said, ‘Your name is possibly out there. We’ll know in a half-hour if you’re with us or end up being with somebody else.’

“They called me back, and I ended up being with somebody else.

“The first time (you’re traded) is always hard. You have a little pity party for a second or two. Then you think, now is a great opportunity.”

Masterson was 12-10 last year with a 3.21 ERA in 216 innings. He was named the opening-day starter this year and is 1-2 with a 4.89 ERA. Toss out one horrible start in Seattle, and the ERA is 3.49.

“It was really just one inning (six runs). Aside from that, it’s been pretty good,” Masterson said. “We’re doing good. First place. Makes for a fun time.”

Cleveland was looking to rebuild three years ago when it dealt Martinez. Now the Indians lead the AL Central.

Martinez played 183 games for Boston and batted .284 with 28 home runs. Boston made the playoffs in 2009 and was swept in the first round, and did not reach the playoffs in 2010.

Martinez then became a free agent and signed with Detroit.

The Red Sox received two extra first-round draft picks when Martinez signed with the Tigers because he was a Type A free agent. With those picks, the Red Sox picked up Matt Barnes and Henry Owens, currently among the top pitching prospects in their system.

So the trade may still work out.

For the players traded, they have to move on from their goals of being regulars at Fenway Park.

When Masterson helped Boston stay alive in the 2008 American League Championship Series, with a 1.59 ERA in five games, he looked like a lock for the Red Sox future.

“The organization gets you in the mind-set,” Masterson said. “They tell you when you get up there, you could be that mainstay.”

But more prospects are traded than actually stay in Boston. Since last July, the Red Sox have traded eight former Sea Dogs — Yamaico Navarro, Chih-Hsien Chiang, Tim Federowicz, Stephen Fife, Jed Lowrie, Kyle Weiland, Josh Reddick and Michael Bowden.

This year, Sea Dogs fans are watching prospects like outfielder Bryce Brentz and pitcher Stolmy Pimentel. Anthony Ranaudo, a top pitching prospect, has just joined the club, and Barnes could be here before the end of the season.

Will they eventually be Red Sox stars, or trade bait?

Several factors determine their future in Boston. In Masterson’s case, it was the desire to add Martinez’s bat to a faltering lineup.

Shortstop Hanley Ramirez, who played in Portland part of 2004 and 2005, was a can’t-miss prospect. But there were questions about his maturity — would he survive the spotlight of Fenway Park? Boston might have kept him, but the Red Sox needed pitching and Josh Beckett was on the trading block.

First baseman Lars Anderson, like Ramirez, was once considered Boston’s No. 1 prospect after batting .316 in Portland with five home runs over the last 41 games of the 2008 season.

There was speculation that Anderson would begin the 2009 season in Portland, with plans for an early promotion to Triple-A and an eventual call-up to the majors.

But Anderson’s disdain for the attention heaped upon him affected his game. He stayed in Portland the whole season, batting .233 with nine home runs. He was almost traded last season for Oakland pitcher Rich Harden, but Boston backed out, fearful of Harden’s health.

But with Adrian Gonzalez playing first base for Boston, Anderson’s time in the organization might be running out.

Jed Lowrie, a Sea Dogs standout in 2007, started at shortstop for the Red Sox in the 2008 playoffs and was the opening-day shortstop in 2009. But injuries have been a persistent problem. He was dealt in the offseason.

Prospects don’t think of trades when they come up through an organization. But then they happen. And, Masterson said, it’s not a bad thing.

“You’re traded. Usually, someone wants you,” Masterson said. “They expect great things out of you, just as you do for yourself. That’s what you aspire to, until you probably get traded again, someday.”

Staff writer Kevin Thomas can be reached at 791-6411 or:

[email protected]

Twitter: ClearTheBases