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07/29/12 8:44 PM ET

Zimmerman on a torrid run through July

MILWAUKEE -- Washington has had the National League's best offense in July, and Ryan Zimmerman has been the hitter most responsible for that offensive outburst.

The Nationals entered Sunday's game at Miller Park having scored 121 runs in July, behind only the Twins' 123 for the Major League lead. Zimmerman has played a big role in that success, driving in 24 runs this month while posting a .368/.439/.768 batting line. He leads the NL this month in RBIs and runs scored, and he's second in hits and homers.

The third baseman has hit eight doubles and 10 homers in July, becoming just the third Nationals player since 2005 to record double-digit homers in a single month. The only others were Alfonso Soriano, who did so with 12 in May 2006 and 11 that August, and Adam Dunn, who hit 10 in May 2009.

In 31 games since he received a cortisone shot in his right shoulder June 24, Zimmerman is hitting .362 with a 1.158 on-base plus slugging percentage, 11 doubles, 12 homers and 33 RBIs.

Nats lose LaRoche to recurring back tightness

MILWAUKEE -- Nationals first baseman Adam LaRoche left Sunday's 11-10 win over the Brewers in the middle of the fourth inning due to back tightness, and had "no clue" if he'll be ready to go in Tuesday's series opener against the Phillies.

The Nationals said LaRoche is day to day with the injury, but he has been dealing with lower-back soreness for a week or two. He has been able to deal with it by spending time before each game focusing on getting it stretched out and ready to play, and it hasn't bothered him at all while hitting. But with the short turnaround from Saturday night's game, LaRoche couldn't get it as loose as he'd like to, and he told the staff before the game it was particularly sore.

"I felt like it was kind of going the other direction today," LaRoche said. "I felt like the more I stood around in the field and sat on the bench, the tighter it was getting. Hopefully tomorrow, having a day off can get it feeling better."

He went 1-for-2 with a single in two at-bats before exiting. He didn't think it was severe, and a doctor told him it was strictly a muscular issue -- there was no nerve damage or anything more serious. But when manager Davey Johnson heard LaRoche say during the game his back was tightening up, he knew he had to take him out.

"I can't lose him," Johnson said. "He's pretty durable. He never says anything, never comes out of the ballgame. When I heard that he had a problem, I immediately made the change."

Harper overcomes stomach virus to start

MILWAUKEE -- Bryce Harper said on Saturday night that he'd be back in the Nationals' starting lineup for the series finale at Miller Park, and indeed he was.

Nationals manager Davey Johnson slotted Harper back into the second spot of the order and started him in right field for Sunday's game against the Brewers and right-handed starter Mark Rogers.

The rookie outfielder was a late scratch from Saturday's lineup due to a stomach virus. Harper revealed after the game that he hadn't been able to keep food down from Thursday night until Saturday afternoon, and he felt lightheaded and dizzy as a result.

Harper was vomiting late into the night Thursday and Friday -- even during Friday's game -- and a doctor told him and Johnson that the rookie would be best served to sit out Saturday. Harper said he felt better and had been keeping food down after Saturday's game, but he was still "a little jittery and whatnot."

Worth noting

• The Nationals signed free-agent right-hander Mike MacDougal to a Minor League contract and assigned him to Triple-A Syracuse. The 35-year-old reliever made seven appearances for the Dodgers this season, posting a 7.94 ERA. He went 3-1 with a 2.05 ERA over 57 innings last year for Los Angeles.

• The Nationals unconditionally released outfielder Xavier Nady on Sunday. Nady was designated for assignment on July 21 when Washington recalled left-hander John Lannan. The 33-year-old was sidelined by a right wrist injury and batted .157 in 40 games with the Nationals this season.

• With their 60th win of the season on Saturday night, the Nationals became the first Washington-based team to win at least 60 of their first 100 games since the 1933 Senators (64-36), according to the Elias Sports Bureau.

The Nats have also already won more games this year than they did in 2008 or '09, when they won 59 games each season.

• Saturday night's 4-1 win over the Brewers was Johnson's 100th as the Nationals' manager. Johnson carried a 100-83 record with Washington into Sunday's series finale at Milwaukee.

Adam Berry is a reporter for MLB.com. Follow him on Twitter at @adamdberry. This story was not subject to the approval of Major League Baseball or its clubs.