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5/22/2014 3:50 P.M. ET

Pierzynski gets rare start with Lester on hill

BOSTON -- For just the third time in 10 starts this season, Jon Lester had A.J. Pierzynski as a batterymate instead of David Ross for Thursday's game against the Blue Jays.

Dating to the latter portion of last season, Lester and Ross have worked well together. In his first two starts this season with Pierzynski, Lester had a 3.86 ERA and a .347 opponents' batting average. With Ross, he has a 2.39 ERA and a .194 average.

Why the switch?

Pierzynski is 9-for-22 lifetime (.409) against Mark Buehrle, his longtime batterymate with the White Sox.

"He's had quite a bit of success against Buehrle and in a stretch where we're trying to generate as much offense as possible," Farrell said. "That's where we are in the lineup today."

Of late, Ross has struggled mightily at the plate, providing just three hits in his last 27 at-bats.

Red Sox feel fixing delivery key for Buchholz

BOSTON -- The early-season slump of Clay Buchholz is not something the Red Sox are taking lightly. Following Wednesday's loss by the right-hander, manager John Farrell and pitching coach Juan Nieves labored over game film looking for answers.

"Well, we spent quite a bit of time here last night doing just that," Farrell said. "There are some things we need to work on from a delivery standpoint. Physically there are no complaints. There are no restrictions. And yet we've got to get him in a position in his delivery more consistently."

Prior to Thursday's game, Farrell and Nieves took their findings and discussed them with Buchholz, hoping it might help the righty have an improved outing on Monday in Atlanta.

"Well, he's not repeating his delivery right now," Farrell said. "So when he's making mistakes, he's been up in the strike zone or he's been in the middle of the plate. And last night, more than we've seen this season, he pitched behind in the count a lot. And again, that's from repeating a delivery, or lack of repeating his delivery as much as needed."

How is Buchholz holding up from a mental standpoint?

"He knows he's better," Farrell said. "He's disappointed in what's taken place so far. There have been glimpses, or there have been individual games where it's been more Clay-like. He knows he's got to improve."

At this time last year, Buchholz was arguably the best pitcher in the American League. Through his first nine starts of 2013, Buchholz was 6-0 with a 1.78 ERA. This year, Buchholz is 2-4 with a 6.32 ERA through the same amount of starts.

"Yeah, he's not in the most confident state as we've seen," Farrell said. "If you compare right now to this time last year, there's some differences. Gradually, pitch by pitch, not to be cliché, but pitch by pitch we have to rebuild that confidence."

Napoli sidelined by illness for finale vs. Jays

BOSTON -- For the second straight day on Thursday, the Red Sox were without cleanup hitter Mike Napoli, who is under the weather.

"Improved today," manager John Farrell said before the series finale against Toronto. "Still dealing with some dehydration. Still dealing with overall achiness and some nausea. We're hopeful at some point later this afternoon there may be the availability in today's game."

The absence of Napoli gave Mike Carp the chance to start two days in a row at first base.

Carp belted two doubles in Wednesday's 6-4 loss, showing flashes of the player who seemed to come up big every time he got a start in 2013.

"There's no hesitation [playing Carp]," Farrell said. "We're comfortable putting any guy in our roster in the lineup when called upon or when needed. We're fortunate that we do have some depth. We can go to a quality at-bat. I think as he's starting to show, the more consistent at-bats of late are starting to pay off with some timing and some hard-hit balls like last night."

Sox planning for Drew's Minor League rehab

BOSTON -- The Red Sox are still in the process of finalizing plans for Stephen Drew to go on a Minor League rehab assignment.

The shortstop was again at Fenway Park on Thursday and worked out under the watch of the club.

Drew will occupy a Major League roster spot until the Red Sox send him out, which means the move will likely happen soon, perhaps as early as Friday.

Manager John Farrell said that the Red Sox would likely use Drew's roster spot for a reliever for the next two games, and then for a starting pitcher to replace the injured Felix Doubront on Sunday.

As for Drew, the Red Sox are weighing several things before deciding which affiliate he will go to. After he gets about 25 at-bats, Drew will rejoin the Red Sox.

"We're looking at schedules, we're looking at who is in certain cities," Farrell said.

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.