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4/6/2014 7:46 P.M. ET

Arrieta works three hitless innings at Double-A

CHICAGO -- Cubs pitcher Jake Arrieta, rehabbing from tightness in his right shoulder, gave up one run and took the loss in his first Minor League rehab start for Double-A Tennessee on Saturday.

The Smokies lost, 5-0, in a game shortened because of rain. Arrieta walked a batter, and the run scored on a wild pitch. He struck out three and threw 42 pitches, 28 strikes, in three innings.

Cubs manager Rick Renteria said he received good reports on Arrieta, who did not pitch in any Cactus League games this spring.

There is no timetable for Arrieta's return, and he was expected to make at least two more Minor League starts.

Castro bats sixth, welcomes opportunity for RBIs

CHICAGO -- Starlin Castro has batted second and third this season, but on Sunday, Cubs manager Rick Renteria dropped the shortstop to the sixth spot in hopes he could drive in some runs. It worked.

Castro delivered an RBI double in the Cubs' four-run first of an 8-3 victory over the Phillies.

The Cubs entered Sunday 4-for-40 with runners in scoring position through their first five games.

"It's good, because we haven't scored any runs," Castro said of the switch. "That's why I'm going to try to do something to get some more runs. It's good. I feel good. That's a RBI position. Maybe we'll have men on base in scoring position."

Renteria also wanted to take advantage of Castro's numbers against Phillies starter A.J. Burnett. The Cubs shortstop is now 10-for-25 in his career against the right-hander.

The Cubs manager didn't talk to Castro before posting the lineup.

"He's not a guy I worry about," Renteria said.

Castro understood the switch.

"We haven't scored runs," Castro said. "I take [batting sixth] in a good way. We've left a lot of people in scoring position. I know Ricky is trying to do something."

Baez homers for Triple-A Iowa to end slide

CHICAGO -- Top prospect Javier Baez ended his hitless streak at Triple-A Iowa in style on Sunday with a pinch-hit home run in the seventh inning.

Baez was hitless in his first nine at-bats at Iowa and was ejected from Saturday's game after arguing a checked-swing call on strike three.

"Javy probably should have gotten thrown out," Iowa manager Marty Pevey told the Des Moines Register after Saturday's game. "As soon as he throws his hands up in the air, you're gone."

Baez struck out six times in his first nine at-bats.

"He's frustrated," Pevey told the Register. "There's frustration there. Anybody that competes is going to react that way. He's got to understand that all his teammates have his back and we understand."

Cubs manager Rick Renteria saw Baez quite a bit this spring and agreed Sunday that the shortstop is probably frustrated.

"They're all young and trying to get through their growing pains," Renteria said Sunday. "I think it's part of the process. I think he'll overcome it and get better and learn from it and keep moving forward."

Extra bases

• Outfielder Darnell McDonald, 35, who was in the Cubs' Spring Training camp, has announced his retirement after 15 years in baseball. He posted this on Instagram: "After playing [15 years] professionally I'm humbled to announce that I'm hanging up my spikes. When one dream ends a new one begins. BIG thanks to everyone that has helped me fulfill my dream of playing in the show."

McDonald batted .222 in 15 games this spring. He played for the Orioles, Twins, Reds, Red Sox, Yankees and Cubs, and finishes with a career .250 average.

Carrie Muskat is a reporter for MLB.com. She writes a blog, Muskat Ramblings, and you can follow her on Twitter @CarrieMuskat. This story was not subject to the approval of Major League Baseball or its clubs.