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6/9/2013 1:02 P.M. ET

Harvey expected to make next start on Thursday

NEW YORK -- At some point down the line, Matt Harvey might pitch in a much more meaningful game for the Mets. When that time comes, manager Terry Collins said Sunday, the team could be able to turn its head if its pitching stud feels some discomfort or slight pain.

For now, though, the Mets aren't going to let Harvey pitch through anything.

"We can't risk this guy getting hurt," Collins said. "It would be one of the worst decisions you can make to let this guy go out there, as competitive as he is, and pitch with a possible injury that could not only hurt his back even worse, but have him change his delivery where he could hurt his arm."

So that's why Collins took Harvey out of Saturday's game after Harvey felt some discomfort in his lower back while warming up for the eighth inning. Harvey received treatment immediately, which essentially realigned his hips. He was confident he would make his next start.

Now the Mets are, too.

Collins said Sunday that Harvey is fine, and will be able to start on Thursday against the Cardinals. He said Harvey actually told the team that he wished he had said something earlier in Saturday's game so he could've taken care of the problem between innings and continued to pitch.

Harvey said he woke up Sunday without any pain.

"Everything's normal, everything's fine," Harvey said. "I woke up today and didn't feel anything. We're good to go."

With Harvey pitching Thursday's game, Shaun Marcum will start Friday against the Cubs. Marcum threw eight innings and 105 pitches in relief in Saturday's 20-inning marathon that ended in a 2-1 loss for he Mets.

He actually pitched longer than Harvey did. Harvey went seven innings and threw 93 pitches, so Marcum will get the extra day of rest.

Meanwhile Jeremy Hefner will start Tuesday against St. Louis, while Dillon Gee will be on the mound on Wednesday.

The Mets certainly breathed a sigh of relief that Harvey is good to go.

"I'm ready to go," Harvey said.

Davis one of three demoted as Mets shake up roster

NEW YORK -- After the Mets' 8-4 loss to the Marlins on Sunday, Terry Collins said patience was running low and significant changes might be in order. New York has dropped five of its last six games, including four to the Marlins -- who have the worst record in baseball -- and the Mets have fallen to 12 games below .500.

Too many blunders on the basepaths, too many poor at-bats and too many missed opportunities have brought the Mets to their lowest point yet.

"Are we starting to run out of patience?" Collins said. "Yeah."

And just minutes after Collins addressed possible changes, the Mets shook up their roster.

New York optioned first baseman Ike Davis, outfielder Mike Baxter and reliever Robert Carson to Triple-A Las Vegas. General manager Sandy Alderson said the Mets' problems aren't a reflection of the coaching staff.

In corresponding moves, the Mets will call up infielder Josh Satin, outfielder Collin Cowgill and left-hander Josh Edgin from Las Vegas before Tuesday's game against the Cardinals.

"This is not a staff issue," Alderson said. "This is a player issue."

Of the three sent down Sunday, Davis' demotion is the most significant, though it isn't the most surprising. His struggles at the plate have been well documented, and his ability to break out of them has remained elusive.

After going 0-for-3 on Sunday, Davis' average dropped to .161. All season, Davis has tried to remain positive despite the constant questioning and speculation about when he would be sent down to Triple-A.

On Sunday, Davis chose not to speak to reporters about his demotion.

Alderson said this is the time to make the move. Davis clearly wasn't finding a solution while remaining with the Mets.

"I think at some point you just have to say to yourself, 'This is not in his best interest,'" Alderson said. "I was one of his biggest supporters and I just felt that at some point we've got to get him out of here."

Alderson said Davis needs to be able to play every day and work on his swing without having to worry about what the outcome will be.

The Mets five-game winning streak a couple weeks ago briefly overshadowed Davis' struggles. He hit a big, two-run single in the eighth inning against Atlanta on May 26 to help begin that winning streak, and at times since then looked like he was nearing a breakthrough.

But he would quickly fall right back into his slump, again looking overmatched at the plate.

Combined with the Mets beginning to struggle again as a team, the questioning of Davis' future began to resurface.

"He's had a lot of people in his ear talking about his swing and talking about what he needs to get to do to get back to where he was, and some ways maybe this is another way to clear the deck and get to Vegas," Alderson said. "I think the first thing is he needs to get into a different environment, he needs to get his confidence back and he needs to hear fewer voices."

Alderson said there wasn't anything Davis could have done Sunday to stave off the demotion any longer.

Davis is heading to Las Vegas with two players who have also struggled.

Carson gave up a run in the Mets' 8-4 loss to Miami Sunday, swelling his ERA to 8.50. He appeared in 13 games this season, giving up 18 runs (17 earned) on 19 hits in 18 innings. Alderson said he was in the bullpen to take some pressure off fellow lefty Scott Rice, but he wasn't doing that.

Baxter was hitting .212 with no home runs, four RBIs and 20 strikeouts in 85 at-bats. He failed to get down a bunt in a key situation on Sunday, which is something that even Collins acknowledged as unusual.

"Mike Baxter's about as heads-up a player as there is on this team," Collins said. "So when he doesn't get a bunt down, it's pretty surprising."

The changes with the roster, though, aren't surprising.

The Mets' offense has been lackluster all season, and that's only intensified in the team's recent struggles. In their 20-inning, 2-1 loss to Miami on Saturday, New York was 0-for-19 with runners in scoring position.

Changes were inevitable. Three players have been sent down, and three have been called up. Whether or not there are more to follow remains to be seen.

Said Collins: "This is when you reach down inside and you find out who belongs here and who doesn't."

Nieuwenhuis rejoins Mets with improved swing

NEW YORK -- Early on Sunday morning, some time after Kirk Nieuwenhuis arrived in New York at 7:30 a.m. ET and Terry Collins spoke with the media at 10 a.m., the manager and the newest member of his team talked about the outfielder's time with Triple-A Las Vegas.

It's where Nieuwenhuis started to get his swing back, where he found an improved power stroke and where he finally was able to once again get consistent at-bats. He changed some things physically with his swing, he changed some stuff mentally, but most important was the repetition.

"Overall, just the amount of at-bats I got was huge," Nieuwenhuis said. "I think it helped a lot, for sure."

The newest member of the Mets, Nieuwenhuis batted just .232 with the 51s and wasn't in the lineup, but he pinch-hit in the 10th and struck out.

Nieuwenhuis said Collins hadn't discussed the outfielder's role much, but Collins said it "won't be a straight platoon" in the outfield.

"You want to pick your spots, not to put Juan [Lagares] over his head or even Nieuwy over his head against somebody that he's just not going to be able to hit," Collins said.

Nieuwenhuis replaces Rick Ankiel, who was designated for assignment after an 0-for-4 day with three strikeouts in Saturday's 20-inning, 2-1 loss to Miami. Ankiel batted .188 this season (24-for-128), just .098 (8-for-82) since debuting with New York on May 2.

He played 21 games with the Astros before joining the Mets and has struck out 60 times this season.

Nieuwenhuis brings a nearly certain upgrade in terms of consistency, as well as power. He's clubbed 10 home runs in Triple-A, albeit in the hitter-friendly Pacific Coast League, and credits a change in mechanics, approach and repetition -- not beneficial weather.

He said he was taking too many fastballs, especially early in the count, and keeping his front foot a little too close to the mound. As early as Sunday, he'll have a chance to try these adjustments out in New York.

"It's great to be back with my teammates," Nieuwenhuis said. "Hopefully we can get something going here. I know we've got an off day tomorrow, but hopefully we get something going."

Collins reflects on Saturday's 20-inning loss

NEW YORK -- Terry Collins has managed more than 1,200 games in his career, but he had a swift, succinct answer when asked if he'd ever managed a more frustrating game than Saturday's 2-1, 20-inning loss to the Marlins.

"Never," he quickly replied. He never had been in one even remotely close to as frustrating.

"We had so many chances to win the game," the Mets manager said. "You're looking for that bloop single, you're looking for that bad hop that makes a difference."

Those bad hops never came. Neither did the bloop singles -- at least not strung together well enough to do any damage. New York successfully put men in position several times in extra innings, but went 0-for-19 with runners in scoring position and stranded a total of 22 men.

In the bottom of the 12th inning with Daniel Murphy 90 feet from home, Mets outfielder Marlon Byrd lifted a fly ball into right field, deep enough for Murphy to possibly score.

"The throw's off line," Collins said, "the guy scores."

Instead, Marcell Ozuna's throw to the plate was perfectly straight and way ahead of the charging second baseman. Rob Brantly absorbed Murphy's collision to tag him out -- another opportunity squandered for New York.

The loss wasted some remarkable feats, too. David Wright collected three hits, starting pitcher Matt Harvey threw another strong seven innings and Shaun Marcum -- usually a starter -- tossed eight innings of one-run ball in relief and was saddled with his seventh loss of the year. Catcher John Buck is out of Sunday's lineup after catching the full 20 innings of Saturday's loss.

Collins will still have him off the bench if he's needed, but his wasted effort and ensuing day off is one scar of the remarkable loss.

"Catching 20 innings, I was surprised he walked in there this morning. I thought he might have to come in in a cart." Collins said.

"He was good," he added before a pause and a moment to think, then put his reaction to the marathon as matter-of-factly as he could. "That's a long game."

First-round pick Smith takes BP at Citi Field

NEW YORK -- The Mets saw a glimpse of their newest star prospect on Sunday, as first-round Draft pick Dominic Smith was at Citi Field to meet some of the players and take batting practice on the field.

"It's kind of surreal," the 17-year-old Smith said. "I'm just happy to be here, I'm glad to come to New York, my new home."

The 6-foot, 185-pound left-handed-hitting first baseman from Junipero Serra High School in California wore a blue Mets uniform top and white uniform pants. He chatted with some of the Mets in the clubhouse, and then took the field to hit.

General manager Sandy Alderson stood in front of the Mets dugout and watched Smith take batting practice.

Smith said he attended Saturday's 2-1 loss to the Marlins, and stayed for all 20 innings. He also spent the last few days sightseeing around New York City.

"I've enjoyed myself here," Smith said. "I've had a blast so far."

This isn't the first time he's hit in a Major League ballpark. He played in the L.A. City Championship at Dodger Stadium a couple weeks ago, but Smith said of Citi Field, "It's better here."

Smith also took notice of the size of the ballpark. But with a sweet swing that's been getting plenty of attention, Smith might find himself hitting here on a regular basis within the next few years.

"Yeah, it's a big park," Smith said. "I've just got to keep working everyday to get better. I'm just very excited to be here."

Chris Iseman and David Wilson are associate reporters for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.