The move paid off as LaRoche hit his 15th home run of the season in the sixth inning to help lead the Nationals to a 3-0 win over the Milwaukee Brewers.
Prior to the home run, Washington's first baseman had just one hit in his previous 28 at bats. LaRoche said Ian Desmond suggested he try Werth's bat as Werth was hitting .337 in his last 51 games.
"My bat has not been feeling very good lately so why not give someone else's a try," LaRoche said. "I got a pitch I could hit and I was able to drive it."
Desmond, who batted after LaRoche, also used Werth's bat, but he flied out to leftfield.
"Maybe we should just leave Jason's bat up there for everyone to use," LaRoche said.
The other key to the game for the Nationals was the continued strong pitching of Dan Haren. He went seven strong innings, giving up just four hits, with six strikeouts and two walks.
The only inning that Haren struggled was the first as he gave up a leadoff double to Rickie Weeks. Weeks moved to third on a sacrifice bunt. Haren struck out Jean Segura, but walked Jonathan Lucroy. He got Carlos Gomez to pop out to short to end the inning.
It was the second straight strong outing for Haren (6-11) as he allowed one run and three hits in seven innings of a 4-1 win over the New York Mets on July 27. Prior to that, Haren had not won a game in more than two months as the Nationals had lost his previous 11 starts. Haren went 0-8 with a 6.18 ERA in that stretch.
Haren was on the disabled list in early July with a sore right shoulder and said the rest did him good.
"Going on the disabled list gave me a chance to regroup," he said. "I wanted to leave the first part of the season behind and help the team try and get back into the race."
Nationals manager Davey Johnson said Haren has a lot of pride and wanted to help the team win.
"He threw a bunch of pitches early, but really settled down," Johnson said. "He's been throwing very well for us."
Johnson said Werth left the game in the sixth inning after injuring his groin. Werth is not expected to play Sunday, but Johnson said he hopes to play him on Monday against Atlanta.
Donovan Hand (0-3), making his sixth start of the season, gave up three runs on five hits for the Brewers.
Milwaukee lost its third straight game and has only scored one run in the first two games of the series.
Brewers manager Ron Roenicke said it was another game of wasted opportunities.
"When we get these opportunities, we need to figure out a way to get those guys in," he said. "We didn't have a lot today but when we do have the opportunity (in the first inning) -- and at that point a ground ball to the infield scores the guy --we have to find a way to put it in play. "
The Nationals took a 1-0 lead in the second inning. Werth singled to start the inning and scored on Anthony Rendon's sacrifice fly as he slid around the tag from Lucroy.
Wilson Ramos' seventh home run of the season in the fifth inning boosted Washington's lead to 2-0. LaRoche's home run in the sixth inning closed out the scoring.
Notes: Roenicke said LHP Tom Gorzelanny is expected to miss at least one start after being struck on his pitching elbow by a line drive Friday night. ... The attendance for the first two games of the series was 70,514, meaning the team handed out $705,100 in vouchers for food and merchandise. The team is handing out $10 vouchers to every fan that attends a home game in August as a result of slugger Ryan Braun's suspension for the rest or the season. ... Brewers RHP Kyle Lohse (7-7) will pitch the series' finale Sunday against the Nationals' RHP Taylor Jordan (1-3).