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4/21/2013 2:14 P.M. ET

Mets recall Carson, designate Laffey for assignment

NEW YORK -- Unhappy with their current bullpen mix, the Mets made a move Sunday morning to bring in a fresh arm, recalling left-hander Robert Carson from Triple-A Las Vegas. Once considered a favorite to make the Opening Day roster, Carson posted a 1.17 ERA over 7 2/3 innings with Las Vegas, striking out seven against two walks.

"He's been throwing very well," manager Terry Collins said. "Rob gives us another option, especially against a team like the Nationals that have so many left-handers in the middle of their lineup. They're all good hitters. But we need to just have a left-hander available that if you're going to get beat, you want them to get beat by somebody who doesn't hit them very good."

To make room for Carson, the Mets designated struggling lefty Aaron Laffey for assignment -- the strongest indication yet that Shaun Marcum will be ready the next time the Mets need a fifth starter on Saturday. Laffey had been Marcum's replacement in the rotation, posting a 7.20 ERA in two starts and two relief appearances.

"It's been tough for him," Collins said. "But we just thought it was important to bring up a relief pitcher, so we did."

That reliever is Carson, who seemed on track to make the team before the Mets broke camp with Scott Rice instead. Carson and Rice give Collins multiple left-handed options outside of Josh Edgin, who has given up seven runs over his last three appearances.

Should that trend continue, Edgin may rapidly lose work to Carson.

"I was disappointed in myself when I got the news, but I knew I had to keep working," Carson said of not making the club initially. "So I went down and went back to the drawing board and kept working, and got all my stuff consistent down there and tried to command the strike zone. And that's what I did."

Marcum on track to make Mets debut Saturday

NEW YORK -- Right-hander Shaun Marcum is scheduled to throw up to 75 pitches Monday, putting him on track to make his Mets debut Saturday.

If Marcum completes his work without any setbacks, the Mets will activate him in time for a 1:05 p.m. ET game against the Phillies at Citi Field. Marcum has been on the disabled list since Opening Day with nerve inflammation in his neck.

"We'll see how he gets out of tomorrow," manager Terry Collins said Sunday morning, "but that would put him on course to be in the spot when we need him."

Should Marcum indeed debut on Saturday, he will be limited to less than 100 pitches as he continues to work his arm back into shape. But the Mets still feel Marcum can give them a stronger effort than left-hander Aaron Laffey, who was designated for assignment Sunday morning following two ineffective starts.

"Shaun's getting ready," Collins said. "He'll be treated like it's his first start of the year pretty much. But the kind of pitcher he is, you look up at 90 pitches and he's in the seventh inning. He's a guy that pitches to contact. ... He's not a ground-ball guy. We'll wait to see how he comes out of tomorrow, but if he's ready, I think he'll give us what we want, and that is a guy to come in and eat up some innings for us."

Collins decides to keep Duda in No. 6 hole

NEW YORK -- Lucas Duda entered Sunday's play leading the National League in OPS, the statistic that perhaps best encapsulates a power hitter's value. So it was only natural that in his daily staff meeting, manager Terry Collins considered moving Duda from sixth to fourth in the starting lineup.

Ultimately, the move never happened. Wary of affecting Duda's mindset, Collins opted to keep Duda sixth and Ike Davis cleanup, despite the latter's season-long slump.

"This game is about confidence," Collins said. "Lucas Duda is feeling pretty good. I don't want to change that. One thing I don't want to do right now is put him in a situation where he thinks he's got to do more than he's doing at this particular moment."

What Duda is doing is precisely what the Mets hoped when they named him a full-time outfield starter. Entering Sunday's play with a league-best 1.199 OPS, Duda also ranked third in the NL in on-base percentage, third in slugging and tied for ninth in home runs, with more walks (14) than strikeouts (12).

Compare that to Davis, who was hitting .161 with a .575 OPS, despite batting exclusively cleanup against right-handed pitchers. Davis' two-homer game Friday apparently did not spark him, as he finished 0-for-4 with three strikeouts the following afternoon. More than a quarter of his plate appearances have ended in strikeouts.

But despite the stark contrast between Davis and Duda, Collins was unwilling to make a swap.

"If you start juggling your lineup all around, when these guys come to the ballpark they don't know where they're at," the manager said. "I'm feeling pretty good where Lucas is in the lineup, so I just want to leave him there.

"A lot of it has to do with the fact that this guy's confidence is pretty high right now. He's feeling good. I don't want him to all of the sudden be slapped in the four spot and have an 0-fer and think he's hurt the club. I just want to leave him where he's at."

Anthony DiComo is a reporter for MLB.com. Follow him on Twitter @AnthonyDicomo. This story was not subject to the approval of Major League Baseball or its clubs.