The Red Sox placed pitcher Josh Beckett on the 15-day disabled list Wednesday afternoon, one day after he left a start against the New York Yankees with a lower back strain.

Beckett, who missed his previous start with the same injury, left Tuesday's game in the fifth inning after giving up five runs (three earned) on five hits in 4 2/3 innings. He said he aggravated the injury throwing a pitch to Alex Rodriguez in the fifth, and was removed after the next batter.

"We thought about bumping him back, have him miss a start, but if we put him on the DL he can basically miss one start and we can line him up to where he comes off the day he is eligible," said Red Sox manager Terry Francona.

The skipper said that he did not want to risk Beckett overcompensating for the back and injuring something else. Beckett would actually miss a second start, but with a day off on May 31 could be in line to come off the DL and pitch against Oakland on his regular turn June 3.

The move is the latest setback for Beckett, who leads American League pitchers with 37 earned runs allowed. He first hurt his back swinging a bat in the cage as the pitchers prepared to hit in the team's upcoming series in Philadelphia.

In order to fill Beckett's roster spot, the Sox called up reliever Joe Nelson from Triple-A Pawtucket and will insert Tim Wakefield back into the rotation. Wakefield, who has allowed five runs in 13 2/3 innings over his last two starts, will get the nod in Beckett's place Sunday against the Phillies.

Nelson, who pitched effectively in spring training and was in the mix for the last bullpen spot, was 3-2 with a 2.49 ERA in 16 games out of the bullpen for the PawSox. He said that losing out on an Opening Day roster spot actually allowed him to hash out a few issues at the Triple-A level.

"I got to work on a few things. In spring training when you're in competition you just get out there and compete and it came down to the last day," Nelson said after settling into the Red Sox clubhouse Wednesday. "I actually had a chance to breathe down in Triple-A and work on a few things and it's gone pretty well."

The 35-year-old said he has worked on a slide step to home plate, as well as improving his breaking ball and fastball command. Francona is confident to have a guy who won't be intimidated by the stage.

"We asked him to go to Triple-A, he went and did a great job and now he's that guy that we need help, he's a veteran presence where this place won't throw him," Francona said. "He can compete and if he gets an out, good, if he doesn't it's not because he's nervous or he's scared, he should be able to help us."

Nelson pitched in three games for Boston back in 2004.