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05/03/12 1:36 AM ET

Prior inks Minor League deal with Boston

BOSTON -- Mark Prior, who was once an ace for the Chicago Cubs, is attempting another comeback -- this time with the Red Sox.

Prior, thanks to a barrage of injuries, hasn't pitched in the Major Leagues since 2006. The right-hander will start out in extended spring games pitching out of the bullpen.

"We signed Mark Prior to a Minor League deal," said general manager Ben Cherington. "He's been in Fort Myers for a while, working out and throwing in extended games. He looked good, the velocity's been good. He's coming off a groin procedure this winter, so we're going to leave him down there for a while just to build strength before we send him out to a Minor League club. He signed a Minor League deal and will keep pitching in extended [spring games] for a while."

Prior, 31, is 42-29 with a 3.51 ERA in 106 Major League outings, all of which have been starts.

Mortensen turns in dazzling debut out of 'pen

BOSTON -- Uncomfortable with an 11-man pitching staff for any longer than a day or two, the Red Sox recalled right-hander Clayton Mortensen from Triple-A Pawtucket prior to Wednesday's game against the Oakland Athletics.

As it turns out, Mortensen was far more than roster filler.

If the Red Sox had been able to pull out a comeback victory, Mortensen would have been one of the prominent figures. Instead, he was a footnote in a 4-2 loss to the A's.

All Mortensen did was reel off three brilliant innings, allowing one hit and no walks while striking out six.

"When you haven't seen a guy, you're pulling for him, but you really don't know what to expect and you have to protect against something that might happen," manager Bobby Valentine said. "He was fantastic. His offspeed stuff in the bullpens in Spring Training looked terrific. Then in the games he seemed to elevate a little. Often we said if it's down, it's really tough. It was down tonight and it was really tough."

Mortensen replaced first baseman Lars Anderson, who was optioned back to Pawtucket after Tuesday's game, on the 25-man roster.

A right-hander who was starting at Pawtucket, Mortensen is the player the Red Sox acquired from the Rockies in exchange for Marco Scutaro back in January.

"He was scheduled to start Thursday, so he was the most rested arm that they had at Triple-A who is on our roster," said Valentine.

Mortensen, who has pitched in 23 Major League games, is excited for the opportunity in Boston.

"It's awesome. It's great to be up here. I'm excited, really excited," Mortensen said.

It remains to be seen how much longer Mortensen will be on the roster, but he showed Wednesday that the team might want to think twice before sending him back down.

"I'm just trying to do my thing," Mortensen said. "Hopefully I do stay and if not that's fine, keep working down there and get back up here."

Crawford, Ellsbury, Kalish making progress

BOSTON -- While the Red Sox's current outfield quartet of Cody Ross, Marlon Byrd, Ryan Sweeney and Darnell McDonald has been holding down the fort pretty well, the rehabbers are making progress of their own.

This includes Ryan Kalish, who hasn't played in the Major Leagues since 2010 because of a series of injuries related to a collision last season at Triple-A Pawtucket.

"Kalish is hitting on a field and throwing out to 120 [feet]," said general manager Ben Cherington. "He's coming along well."

When will Kalish start playing in games?

"No decision on that yet, but he's coming along and hitting on a field," Cherington said. "We'll let him do that for a while and then get him live BP and then get him into game action down there. No timetable on him."

Jacoby Ellsbury, who went down with a partially dislocated right shoulder in the April 13 home opener, is also making good strides.

"Ellsbury's been making progress," said Cherington. "He has a lot more range of motion and soreness is going away. We just need to get full range of motion and a little bit of strength before he can really get into baseball [activities]. He's coming along and feeling better."

What about Carl Crawford, who has a UCL sprain in his left elbow?

"He's not throwing yet," Cherington said. "He has not started swinging yet. He's going to get checked a few days from now, and if he's doing well, he'll start some of that activity. We're just trying to keep his legs going as best as we can."

Ian Browne is a reporter for MLB.com. Read his blog, Brownie Points, and follow him on Twitter @IanMBrowne. This story was not subject to the approval of Major League Baseball or its clubs.