BOSTON -- The Twins traded third baseman Danny Valencia to the Red Sox today for Jeremias Pineda, a 21-year-old outfielder from the Dominican Republic who was playing in the rookie-level Gulf Coast League.

The Red Sox, who have a rookie standout at third base in Will Middlebrooks, immediately optioned Valencia to Class AAA Pawtucket. The Twins assigned Pineda to their GCL affiliate.

Then, in another surprising twist, the Twins promoted Tsuyoshi Nishioka from Class AAA Rochester to fill Valencia's spot on their 25-man roster. Nishioka was batting .245 for the Red Wings.

Pineda, 21, was batting .421 (56-for-133) with nine double, three triples and 14 stolen bases for the Red Sox GCL affiliate.

"Our staff's obviously seen him a lot because we play them a lot [in the GCL]," Twins assistant general manager Rob Antony said. "I saw him for a few games last week. He can run, he can throw, he can hit."

Still, at age 21, Pineda was one of the oldest players in the GCL, so this was a sign of how far Valencia's stock has fallen. After serving as the Twins regular third baseman for much of 2010 and all of 2011, Valencia got demoted to Class AAA Rochester this May and fell behind Trevor Plouffe on the depth chart.

Plouffe is on the disabled list with a bruised right thumb, but the Twins decided they were better off using Jamey Carroll at third base than continuing to use Valencia, who was clearly pressing in the chances he got. Valencia batted .198 with two homers and 17 RBI in 34 games with the Twins this year.

Since the July 31 non-waiver trade deadline has passed, the Twins placed Valencia on waivers, and the Red Sox made a claim. The team finalized the deal today.

"It wasn't a matter where we were down on him or anything else," Antony said. "It was just a situation where this might be a better opportunity for him."

Valencia declined comment through a Twins spokesman.

Plouffe has 19 home runs in 74 games, and the Twins believe he's got a chance to hold down third base for a while.

"I don't think we ever want to hand anybody a job, but Trevor has done a pretty good job over there," Antony said. "He's kind of established himself. ... You can read into it how you want. But we're pleased with what Trevor has done."