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07/22/12 7:35 PM ET

Mendonca adjusting to Triple-A pitching

ROUND ROCK, Texas -- In Double-A Frisco last season, Tommy Mendonca was an All-Star. But with Triple-A Round Rock this year, he's still having trouble adjusting.

"The pitching is the main difference," Mendonca said. "Their sequences are not the same as in Frisco. If you've got two balls and no strikes, you're getting a fastball. Here, when you've got two balls and no strikes, you get a changeup or curveball."

Mendonca, who hit .278 with 25 home runs and 78 RBIs for Frisco in 2011, is batting .213 with seven home runs and 27 RBIs with Round Rock. He was placed on the disabled list twice last month, first on June 2 with a head injury and again on June 19 with a left shoulder injury.

"It's been tough this year being on the DL for my head and then being on the DL for my shoulder," Mendonca said. "It's just hard because you want to get something going but you get shut down because you've got to go back on the DL. That's the toughest part."

Primarily a third baseman, Mendonca is also trying his hand behind the plate. He hasn't spent much time at catcher but has been catching bullpens in an effort to become more versatile defensively. Rangers third baseman Adrian Beltre, a three-time Gold Glover, is signed through 2015 while catchers Mike Napoli and Yorvit Torrealba are set to be free agents after this season.

"The past three days, all I've been doing is catching. I believe catching is still in the future," Mendonca said. "At third, you've got Adrian Beltre, who's got three more years and is one of the best, if not the best, third baseman. That's a tough spot to try to take away. With catching, I've got the body and I've got the build for it. Why not try it?"

Moreland ready to begin rehab assignment

ANAHEIM -- Mitch Moreland, who is on the disabled list with a strained left hamstring, will report to Triple-A Round Rock on Monday to begin his medical rehabilitation assignment.

He will play for Round Rock on Monday and Tuesday, and then rejoin his wife Susannah on Wednesday as she prepares to give birth to the couple's first child. When Moreland is ready, he will return to Round Rock to finish out his rehab assignment next weekend. He could be activated off the disabled list by the time the Rangers open a three-game series against the Angels a week from Monday.

"I'm hoping by the end of the week he'll be ready to go," Rangers general manager Jon Daniels said.

That would allow the Rangers to send rookie outfielder Leonys Martin back to Triple-A to start playing regularly again.

Martin is hitless in his last 16 at-bats and was out of the lineup again on Sunday night against the Angels. He hasn't played since last Saturday in Seattle.

"It's not ideal but it's where we are right now," Daniels said. "Hopefully, Mitch is not far away. [Martin] has handled it well. He's gotten his work in and stayed ready."

Napoli back at DH for second straight game

ANAHEIM -- The Rangers' Mike Napoli started for the second straight day at designated hitter, one day after hitting two home runs against the Angels on Saturday. Yorvit Torrealba, who had three hits on Saturday, was back at catcher.

Manager Ron Washington said that the two will be sharing time behind the plate when the Rangers get back to Texas and start playing in the intense summer heat again.

"I just want to give [Napoli] one more day off his legs," Washington said. "Both of them will have to get in that heat when we get back."

Napoli had one hit and two RBIs in his last 25 games before hitting two home runs on Saturday, He also had three hits on Friday night.

"I definitely feel better," Napoli said. "I've been working hard in batting practice and working hard in the cage. I've been putting the work in, I just haven't been carrying it into the game. I'm just trying to relax and have good at-bats."

Napoli now has three multiple home run games against the Angels since joining the Rangers in 2011. In 14 games against the Angels in Anaheim, Napoli was hittiing .434 (23-53) with eight home runs and 12 RBIs entering Sunday night's series finale.

Worth noting

• Yu Darvish, after beating the Angels on Saturday, has 11 wins on the season. That's one short of the club record for a rookie, set by Edwin Correa in 1986 and matched by Kevin Brown in 1989 and Chris Young in 2005.

• Correa also holds the Rangers' rookie record with 189 strikeouts. Darvish has 132.

• Koji Uehara, on the disabled list with a strained muscle in his right rib cage, has still not resumed throwing. Said manager Ron Washington, "He can play long toss, but he doesn't feel right. We've got to wait until he feels right."

• Reliever Mark Lowe, on the disabled list with a strained muscle in his right rib cage, threw off a mound for the first time on Sunday without any problems.

T.R. Sullivan is a reporter for MLB.com. Read his blog, Postcards from Elysian Fields, and follow him on Twitter @Sullivan_Ranger. Christian Corona is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.