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05/04/12 12:09 AM ET

Harper slides up to third in batting order

WASHINGTON -- Almost a week after being promoted to the big leagues, Nationals outfielder Bryce Harper found himself hitting third in the lineup against the Diamondbacks on Thursday.

In the five games he had played entering Thursday's action, Harper was 5-for-13 (.385) with two RBIs. His best game came Wednesday, when he went 3-for-4 with two doubles, two runs scored and an RBI against Arizona.

"Why not?" said manager Davey Johnson after he was asked why he decided to put Harper in the middle of the order. "He is swinging the bat well. He has had quality at-bats. We are trying to put our guys [in the lineup] that are swinging the bats best. ... It was a pretty good choice to me. ... He has the pop, a good eye, he uses the whole field."

The last time Harper hit that high in the lineup was last season when he was with Class A Hagerstown. Harper, 19, didn't know he was hitting third until he was approached by the media before the game.

"That's great, cool," Harper said. "I have no words for that. I just hope I can make something happen and get us going."

Although he is hitting third, Harper said his approach at the plate will not change.

"The only thing that changes [down in the order] is that you watch the pitcher longer than two [at-bats]. I'm trying to go up there [and] get something I can handle and drive," Harper said.

LaRoche scratched with oblique soreness

WASHINGTON -- Nationals first baseman Adam LaRoche was scratched from Thursday's lineup against the Diamondbacks because of right oblique soreness. He is going to miss two to three days, according to manager Davey Johnson.

LaRoche hurt the oblique diving for a ground ball against the Diamondbacks on Wednesday, and started feeling pain during the latter part of that game. He tried hitting off a tee Thursday, and the oblique felt a lot tighter that it did the previous day.

"I hope we caught it early enough to where we can knock it out. Obviously, the timing couldn't be any worse," LaRoche said. "It's not a severe tear, strain or whatever you want to call it, according to our doctors."

LaRoche is the second player on the Nationals to have an oblique injury in less than a week. Infielder/outfielder Mark DeRosa was placed on the disabled list Sunday because of a left oblique strain. DeRosa cannot do any baseball activities for about a week to 10 days.

With LaRoche out of the lineup, Chad Tracy was inserted into the lineup at first, batting fifth. Tracy went 0-for-2 with a walk in the 2-1 win over Arizona.

Espinosa looking to regain early form

WASHINGTON -- Entering Thursday's action, Nationals second baseman Danny Espinosa found himself in a 5-for-38 slump (.132) over his last 10 games.

Espinosa said he has been overly aggressive. He said opposing pitchers are not giving him pitches to hit, because he has been impatient early in the count.

Espinosa believes that he needs to be more selective at the plate. He was doing that early in the season, when he had seven walks in his first seven games, with a .367 on-base percentage.

"I got out of my approach," Espinosa said. "In the beginning of the season, I was putting the ball in play, drawing walks and having good at-bats. I got away from that approach. ... It's something I thought about today. I need to get back to that. I'm definitely in a positive mood right now, and I know I can get back to that and turn things around."

Bill Ladson is a reporter for MLB.com and writes an MLBlog, All Nats All the time. He also could be found on Twitter @WashingNats. This story was not subject to the approval of Major League Baseball or its clubs.