OAKLAND -- After years of struggling to maintain consistency as a starting pitcher, lefty Andrew Miller has thrived in his first full year as a reliever.

Miller entered Monday night's game against the Athletics with a 2-0 record and a 1.89 ERA in 23 outings this season. Opponents are hitting .172 against him.

"One of the MVP's [of our team] thus far," said manager Bobby Valentine. "Everybody talks about our bullpen. Andrew has been able to be durable and be consistently good. He is a presence out of our bullpen, throwing 96 mph with a very good breaking ball."

How has Miller been able to make such improvements?

"He's been effective because our Triple-A guys did a fabulous job of eliminating his windup and eliminating the other motion that he had in his stretch," Valentine said. "And his efficiency of his delivery, I think, has allowed him to be very efficient in the strike zone."

Both Miller and righty reliever Vicente Padilla have done a tremendous job stranding inherited runners.

"It seems they both take a lot of pride in what they're doing and they relish those opportunities," said Valentine. "When I look them in the eye when they come into the game, obviously I'm looking to different sets. One very experienced, one not experienced at all, but I see the same message and that's, 'Give me the ball. I'm ready for the action.'"

Middlebrooks out of lineup, could head to DL

OAKLAND -- Though the Red Sox are hopeful Will Middlebrooks has just a nagging left hamstring injury, there seems to be a good chance the third baseman won't play in this three-game series against the Oakland Athletics.

"The latest on Will is that he feels better today than he did yesterday and better than he expected to be today," said Red Sox manager Bobby Valentine. "That's the only news we have -- that's good. It's not discolored, and that's good, but it's going to be some days [before he can play]."

The way the roster is currently set up, the Red Sox have 13 pitchers and 12 position players. With Middlebrooks out of the mix, Valentine had only two players on his bench -- utilityman Brent Lillibridge and catcher Kelly Shoppach.

The Red Sox will likely add a position player to the roster by Tuesday. The question is this: Does that mean Middlebrooks will go on the disabled list or will the Sox send down a pitcher?

Both scenarios are currently in play.

With the All-Star break coming up next week, Middlebrooks could go on the disabled list retroactive to Monday and he could be activated by fifth game after the break, which is July 17.

If the Red Sox can avoid putting Middlebrooks on the DL, perhaps he could play in this weekend's four-game showdown against the Yankees at Fenway Park.

"We won't let the calendar dictate it," Valentine said. "We'll just see how he feels. Maybe DL, maybe a few days. It's just one of those injuries. I think we've had them before."

Nick Punto filled in for Middlebrooks at third for Monday's game.

Crawford heads to Portland; Ellsbury could follow

OAKLAND -- After an examination in Boston with the team's medical staff, Red Sox left fielder Carl Crawford was given the go-ahead to take his Minor League rehab assignment to Double-A Portland, beginning on Tuesday.

Crawford hasn't played yet for the Red Sox this season, thanks to left wrist and elbow woes. He went 3-for-14 with five walks in five Gulf Coast League games in Fort Myers, Fla.

Jacoby Ellsbury played his third game in the Gulf Coast on Monday and drilled a home run, as well as walking and grounding out. Ellsbury played six innings in center field.

He will serve as the designated hitter on Tuesday in Florida and could join Crawford at Double-A as early as Wednesday.

Outfielder Ryan Sweeney is also making nice progress with his inflamed big left toe. Sweeney could go on a rehab assignment by the time the Red Sox return home from this road trip. Scott Podsednik, who is recovering from a left groin strain, went 1-for-4 and scored a run at Triple-A Pawtucket on Monday. Podsednik could be activated by the start of the series against the Yankees on Friday night.