ATLANTA (AP) – Boston Red Sox third baseman Bill Mueller returned from the disabled list Friday, but the team lost one of its top relievers, Scott Williamson.

Williamson was placed on the 15-day DL with a nerve impingement in his right forearm. Opponents have hit only .097 against Williamson, who had not allowed an earned run in 18 of 21 appearances.

“He’s going to need some down time,” said Red Sox manager Terry Francona, who said Williamson would have been placed on the disabled list even if the team had not exhausted its bullpen in Thursday night’s 13-inning, 5-4 loss at the New York Yankees.

Mueller, who had been on the disabled list since May 20 with right knee inflammation, was in the starting lineup Friday night.

To make room for Mueller, infielder Cesar Crespo was designated for assignment. To fill Williamson’s roster spot, right-handed pitcher Anastacio Martinez was recalled from Triple-A Pawtucket.

Martinez was 2-0 with a 6.52 ERA with Boston from May 21 to June 16.

Also Friday, the Red Sox acquired two pitchers in separate trades with the Chicago Cubs and San Diego Padres.

Boston obtained left-hander Jimmy Anderson from the Cubs and right-hander Brandon Puffer from the Padres. Both players were sent to Triple-A Pawtucket.

The Red Sox sent minor league reliever Andrew Shipman and a player to be named to Chicago.

San Diego will receive a player to be named for Puffer.

Anderson is 25-47 with a 5.41 ERA in 117 career games over six seasons in the majors with the Pittsburgh Pirates, Cincinnati Reds, and Cubs.

Anderson, 28, made at least 25 starts in three straight years with Pittsburgh from 2000-02. He appeared in seven games for the Cubs this season with one save and a 4.66 ERA.

Puffer, 28, has a 4.60 ERA in 90 innings of relief over the past two seasons at the big league level. Boston is his seventh team.

The Red Sox lose 22-year-old Shipman, who had 13 saves for Class-A Sarasota. The right-hander was signed last August.

AP-ES-07-02-04 2009EDT