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7/21/2013 3:30 P.M. ET

Due to Beltran's minor injury, Peterson makes first start

ST. LOUIS -- The first at-bat and first RBI came Saturday for new Major Leaguer Brock Peterson. He had to wait only a day longer to earn his first start.

After hearing Carlos Beltran was feeling a "little achy," manager Mike Matheny took the opportunity to rest the veteran outfielder and insert Peterson, a 29-year-old Minor League journeyman until this weekend. Matheny did not specify what issue was nagging Beltran, though he did add that the right fielder insisted he felt good enough to play on Sunday, if needed.

Instead, Allen Craig shifted to Beltran's spot in right field, while Peterson subbed in as the left fielder. Peterson last played the outfield in 2011, when he was put there for six Independent League games. Prior to that, he played only 22 games as an outfielder in eight Minor League seasons with the Twins.

Also making a spot start on Sunday was Shane Robinson, who, because the Padres sent a left-handed starter to the mound, replaced Jon Jay in center. Robinson entered the day 7-for-38 against left-handers this year.

Matheny trusts Carpenter's self-evaluation

ST. LOUIS -- After publicly expressing frustration with the result of his rehab appearance in Memphis on Sunday, veteran right-hander Chris Carpenter is expected to discuss his take on the outing with the Cardinals on Sunday or Monday. It will be after that meeting that the Cardinals will determine Carpenter's next step.

Manager Mike Matheny said that he had a brief discussion with Triple-A Memphis manager Ron "Pop" Warner on Sunday morning, but he awaited Carpenter's assessment before forming any conclusions.

"I just saw the line," Matheny said. "Right now, our main concern is how he feels. And once again, I trust his evaluation as much as anything. He's a pretty honest evaluator of himself. I'm excited to talk to him and see exactly how he felt."

Carpenter threw 74 pitches (49 strikes) over 3 1/3 innings on Saturday. He allowed nine hits, four earned runs, walked two and struck out two in what was his second Minor League rehab appearance. If he were to continue pitching every five days, Carpenter would take the mound next in Memphis on Thursday.

"I think if he went out there and threw up all zeros and still didn't feel right, that he would still be pretty upset," Matheny said. "We're excited that he had the strength to get through that. I'm more interested in hearing how he felt. Reading some of the quotes made me believe that he didn't think he was real sharp. But it's going to be something that we evaluate after we get a chance to talk to him personally."

Lynn, Matheny meet to discuss approach, emotions

ST. LOUIS -- Unsure whether he had effectively communicated his desired teaching points with Lance Lynn in the past, manager Mike Matheny met with Lynn on Sunday to discuss how the right-hander can better handle himself on the mound in order to maximize his potential, but also to not show up his teammates.

The meeting, which Matheny said was sought out by both sides, was needed after Lynn's ragged night on Saturday. In the loss, Lynn looked out of sorts with his rhythm and was openly demonstrative when defensive plays weren't made behind him. To the latter point, Matheny and several veterans took Lynn aside to remind him that those emotions could be perceived negatively by his teammates.

"Around here, we take a lot of pride in [the] team. We take a lot of pride in how your teammates perceive you," Matheny said. "I've been doing it really trying to help him with how he's perceived by his teammates, and he's been conscious of it. … I'm not asking any of these guys to be choir boys. But I do care very much how they're teammates and how they all get along and the chemistry.

"If he's got to be angry out there [to be successful], then I want him to be the angriest man on the planet. But keep in mind that there are some things that you need to do as far as your teammates are concerned. So let's continue to work on this to figure out how you can keep that intensity, have that emotion, but not in a way where you're perceived by your teammates negatively."

Matheny sees Lynn's biggest challenge as finding the middle ground between maintaining the intensity that has made him baseball's winningest pitcher since the start of last season, and harnessing it to the appropriate degree. On Saturday, Lynn's attempts to curb his emotions resulted in him slowing down the game to a sluggish pace.

"I think yesterday when things didn't go his way, he was trying to keep himself from exploding, and in the meanwhile it slowed down the pace of the game and it came across as bad poise on the mound," Matheny said. "We lose sight that he is a young pitcher. But he's a very young, talented pitcher. We're just trying to communicate in a way that can help him in his career."

These same two issues of intensity and body language were addressed with Lynn last season, and before Saturday, he had seemingly been doing a better job keeping both in check this year. What the Cardinals want to be careful not to do, however, is sap the emotion out of Lynn completely, as it has long been a driving force behind his success.

"He's so intense; a lot like a [Chris] Carpenter," Matheny said. "And if Carp would have done early in his career a lot of things that he did later in his career, he would have had a lot of people talking to him. You can't sit out there screaming at people. That's just part of the learning curve. But you also realize, like we're realizing right now talking to him, that some of that is a part of your greatness. Let's try to nurture that but chip away the things that happen in here."

Matheny emphasized that such one-on-one conversations with a player happen almost daily inside the Cardinals' clubhouse. A day before, it was rookie reliever Carlos Martinez, who heard from Matheny and other veteran teammates after his rough outing on Friday.

"This stuff constantly happens on a good team," Matheny said. "On a bad team, the veterans let the young guys do what they want to and the young guys run amok. You don't see everybody coming together to try and help each other out."

Worth noting

• Prior to Sunday's game, Cardinals players and staff hosted their families on the field as part of the annual "Family Day" event.

• The Cardinals are scheduled to face the following three starters during their upcoming series against the Phillies: Jonathan Pettibone (5-3, 3.89 ERA) on Tuesday, John Lannan (2-3, 3.76 ERA) on Wednesday and Kyle Kendrick (9-6, 3.94 ERA) on Thursday. The Cardinals and Phillies split a four-game series back in April.

• Left-hander John Gast (left shoulder strain) remains on the rest portion of his rehab program. Gast, who went on the disabled list on May 26, has not been cleared to resume light throwing.

Jenifer Langosch is a reporter for MLB.com. Read her blog, By Gosh, It's Langosch, and follow her on Twitter @LangoschMLB. This story was not subject to the approval of Major League Baseball or its clubs.