Neither Gathright nor Miller were on the 40-man rosters, so the Sox transferred outfielder J.D. Drew to the 60-day disabled list and designated Nate Spears for assignment to make room.
The return to the Majors created a bit of a whirlwind for the 30-year-old Gathright, who signed with the Red Sox as a Minor League free agent on Aug. 31 and appeared in four regular-season games with Pawtucket. He spent most of the year in independent ball with the Yuma Scorpions in Arizona.
"It was like three games left in the season and [Jose] Canseco, who was our manager, called my room, and he was like 'I think Boston's in town to come see you,'" Gathright said. "I was like, 'Come on, Jose. It's like three games left.'
"I thought he was messing around, but apparently he was telling the truth and it all worked out. That's basically it. Not a great story, but I'm just happy to be back, because I didn't think it would happen this year."
The speedy Gathright's last stint in the Majors came in 2009, also with the Sox. He's played parts of six seasons in the bigs and stolen 80 bases.
"Joey, the one thing he's here for is to maybe pinch-run," manager Terry Francona said. "He's got that ability to steal a base or score from first on a double. That's basically what they were trying to see, if he could impact a game when he was at Triple-A, and he knows that and did a really good of it. We know him. Maybe he has a chance to pinch-run at some point and win us a game."
Anderson, 23, spent the whole season with Pawtucket and hit .265 with 31 doubles and 14 home runs in 136 games. The 21-year-old Iglesias is in his second stint with the Sox after an early-season callup, and he finished the year with the International League's best fielding percentage (.973) for a shortstop, but a low batting average (.235).
"A little bit more aggressive, hit the ball with a little more authority," Francona said of Iglesias' second-half approach at the plate. "The first half of the year, kind of a hollow batting average. His progression maybe a little different than everybody else's. You may not see everything until he gets to the big leagues."
The 38-year-old Miller went 0-1 with one save, a 4.19 ERA and 11 strikeouts in 45 Major League appearances this season between St. Louis and Toronto. Tazawa, 25, is returning from Tommy John surgery, which he underwent last April.
The roster move for Drew doesn't change much, because he's less than a week away from being retroactively eligible to return. As for Spears, Francona said he wanted "to make sure he understood how he's felt about in this organization. We really like him."