The Red Sox have faded in the AL playoff race while the Rockies are trying to stay close in the NL wild-card chase.
Delcarmen was 3-2 with a 4.70 ERA in 48 games for Boston this season. The right-hander had been especially tough on lefty hitters, holding them to a .165 batting average.
The 28-year-old Delcarmen had been a key member of the Red Sox bullpen for several years, and pitched in Boston's sweep of Colorado in the 2007 World Series.
"Manny wasn't necessarily pitching in the highest leverage situations with us anymore," Boston general manager Theo Epstein said. "We had a couple of guys that passed him on the depth chart."
Epstein said that the Rockies claimed Delcarmen on waivers and the teams were able to work out a deal.
"Manny had a nice career with us," Epstein said. "At times he would go out there with closer stuff."
The Red Sox began Tuesday in third place, seven games behind the Yankees and Rays, who were tied for the AL East lead.
"We need to get really hot make this thing interesting," Epstein said. "Really hot — hotter than we've been at any point during the year."
To replace Delcarmen, Boston recalled right-handed pitcher Robert Manuel from Triple-A Pawtucket. He was 8-2 with a 1.68 ERA and 12 saves with Pawtucket and 0-0 with a 3.86 ERA in five games with the Red Sox earlier this season.
Balcom-Miller is a 21-year-old righty. He went 6-7 with a 3.31 ERA in 19 starts at Single-A Asheville this season. Boston has assigned him to Single-A Greenville.