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9/3/2014 2:14 A.M. ET

Frias, among three callups, slated to start Nats finale

LOS ANGELES -- The Dodgers' September roster continued to expand Tuesday as infielders Miguel Rojas and Erisbel Arruebarrena and right-hander Carlos Frias all rejoined the team.

Rojas and Frias were optioned Sunday with the return of third baseman Juan Uribe and left-hander Hyun-Jin Ryu from the disabled list. Arruebarrena had been optioned a week earlier with the return of shortstop Hanley Ramirez from an oblique injury.

Manager Don Mattingly said Monday that the three players would be returning with Triple-A Albuquerque's season ending. With the additions, the Dodgers' active roster stands at 33 players.

Frias, 24, will make Wednesday's start in place of right-hander Dan Haren, who wouldn't get a full five days' rest with a 12:10 p.m. PT start. It will be his first Major League start.

"We felt like he was a good guy for this 12 o'clock start," Mattingly said. "He's young. He doesn't need sleep."

Rojas, 25, has played 64 games with the Dodgers this season -- including 24 starts at shortstop and appearances at second base, third base and left field. Arruebarrena, 24, is back for his fourth stint with the Dodgers, going 7-for-28 in 12 games.

Struggling Puig sits as Pederson gets first start, hit

LOS ANGELES -- It's a sink-or-swim situation for Yasiel Puig, and manager Don Mattingly said Tuesday that it's time to get Puig swimming again. Meanwhile, Puig's replacement, Joc Pederson, excelled in his first audition.

Mattingly benched the slumping Puig on Tuesday, giving Pederson, the team's No. 3 prospect, his first Major League start against Doug Fister and the Nationals. Pederson batted seventh and played in center field. He collected his first career hit in the second with a bloop single to center off Fister and also drew a walk in the sixth inning in the Dodgers' 4-1 win.

After the game, first baseman Adrian Gonzalez handed Pederson a ball with his name misspelled on it. Gonzalez said it was the "authenticated" version of the ball. Pederson received the real ball a few minutes later.

"Any hit's a hit," Pederson said of his blooper. "It's just nice to get the first one off your chest."

As for Puig, Mattingly said he hopes the time off gives the outfielder a chance to fine-tune. He wouldn't say whether Puig would return to the lineup Wednesday.

"It gives you a chance to work," Mattingly said. "There's a saying, 'You can't see the forest from the trees.' Sometimes you get so close to it and you're trying and trying and you're almost fighting yourself."

Puig is 6-for-47 in his last 13 games. Mattingly said he thinks the length of the season might be impacting him, noting he had similar struggles near the end of last season.

The decision to start Pederson over Scott Van Slyke or Andre Ethier in center was influenced in part by the man on the mound Tuesday -- Clayton Kershaw.

"I think with Clayton, you really try for the most part to play the best defense that you can," Mattingly said. "The one thing about Joc that I think everyone in the organization is pretty much in concert with is that this guy's our best defensive center fielder. So I feel like today, if we're going to play someone in center ... he's a true center fielder. He's probably the only true center fielder we have at this point."

Pederson didn't have a ball hit to him the entire night.

"When you have someone like [Clayton] Kershaw throwing, there's not many balls put in play," Pederson said. "So it is what is. It's good when I'm not getting balls."

Pederson had a pinch-hit appearance Monday, striking out with the tying runs on base to end a 6-4 loss against the Nationals. But Mattingly said the Dodgers are impressed with the way Pederson carries himself and with the "swagger" he has. After Tuesday's game, Mattingly said the 22-year-old reminds him of the Rockies' Carlos Gonzalez.

"He looked good," Mattingly said. "For me, I watch his at-bats, and he just reminds me of CarGo. The same swing. It's got that [George] Brett look. I think he looks good all the time."

However, Mattingly said Pederson's start in center field doesn't put Puig's job in jeopardy.

"Honestly, this time of year, I don't think Yas has to prove anything here," Mattingly said. "I think we all know that he can do it. It's the simple thought of, 'What are we doing to help get him right?'"

Altercation in past, Guerrero eager to help Dodgers

LOS ANGELES -- With a possible callup to the Major Leagues looming, Alex Guerrero's season took a turn at the end of May when a dugout altercation with then-Triple-A Albuquerque teammate Miguel Olivo resulted in Guerrero losing part of his left ear.

Guerrero underwent surgery to repair the damage, and after a lengthy absence, went on to hit .329 with 15 home runs in 65 games with the Isotopes.

On Monday, he earned the call to the Major Leagues that he had been waiting for. It was his first time back with the Dodgers since the season began in Australia.

"Things happen that sometimes shouldn't happen," Guerrero, 27, said through a translator. "But aside from that, it's all in the past. My focus now is to help the team and do the very best job I can."

Guerrero, who signed with the Dodgers in the offseason after defecting from Cuba, said he's tried to "turn the page" since that May incident. For now, he hasn't sought legal action against Olivo, whom the Dodgers released after the altercation.

"In terms of ill will, there's nothing there," Guerrero said. "And legally that'll be something for my lawyers. That's their focus."

Guerrero said he's prepared to do whatever the Dodgers need him to do. He has experience in both the infield and the outfield, but his best tool is his bat.

"If he gets the chance to play, it's an extra bat for me off the bench, it's a guy who's played some second, who's played some outfield, who's played some short, who's played some third," manager Don Mattingly said. "The main thing Alex did was swing the bat down there, and that's the main area where he showed he's ready, so for the most part, we'll see him hitting."

Michael Lananna is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.