DENVER -- Adam LaRoche has been scuffling this month. He hopes one swing will turn things around.
It was the Nationals fourth straight win and increased their NL East Division lead to two games over Atlanta, which lost to Miami on Tuesday.
The win might have come at a cost after third baseman Ryan Zimmerman left the game in the sixth inning with a strained right hamstring. He is scheduled to have an MRI done Wednesday morning.
"It's pretty sore tonight. Get the MRI, get some results tomorrow and see where we're at," manager Matt Williams said. "It's concerning. Anytime you have to leave the game with a hamstring injury it's concerning."
Zimmerman missed 44 games with a fractured right thumb earlier this season but has played well since coming off the disabled list on June 3.
"He's swinging great, playing great, but we have to deal with it," Williams said. "We'll see how he feels tomorrow and what the doctors say."
Ian Desmond followed Monday's 5-for-5 performance with hits in his first two at-bats Tuesday for Washington. He was hit by a pitch in the sixth to reach base safely in eight consecutive plate appearances. The streak ended when he struck out in the seventh, but the Nationals had taken control on LaRoche's three-run homer off reliever Rex Brothers.
It was LaRoche's first home run off a lefthander since May 28, 2013.
"You swing hard enough enough times you're bound to run into somethings. I've been playing long enough to know a lot of times it takes one swing," LaRoche said. "I've been in a rut for a little while, my timing's been out of whack, so this came at a good time."
Tulowitzki is the third Colorado player in two days to hit the disabled list. First baseman Justin Morneau (neck) and reliever Boone Logan (diverticulitis) were put on the DL on Monday, adding to the long list of Rockies out of action.
"It's unfortunate, it's what I'm dealt with, I've been dealt many, many things in my career," Tulowitzki said. "This is just a bump in the road."
Flande started well before faltering in the sixth. He allowed four runs on five hits and walked two in 5 1/3 innings. He left with a 4-2 lead and runners on the corners, but Colorado's bullpen couldn't hold it.
Zimmerman made it 4-3 with a fielder's choice but left the game after hitting the first base bag hard trying to beat out his grounder.
"Guy's just coming back from the DL, getting his swing back and you hate to see that," LaRoche said. "Cross our fingers it's nothing major."
Wilson Ramos tied the game with an infield single, and then the Nationals broke it open in the seventh.
Brooks Brown (0-1) walked Denard Span and Rendon singled. Brothers relieved Brown one out later and LaRoche pulled a 93-mph fastball into the Rockies bullpen to make it 7-4. It was his 13th of the season and his second hit of the night off a lefty.
"When you're facing a bunch of lefties it can get you right again because you have to stay on the baseball," Williams said.
The Rockies took a 1-0 lead in the second on DJ LeMahieu's RBI triple to right. Arenado made it 3-0 in the second with a two-run homer to center. It was his seventh of the season and first since May 5.
The Nationals got two back in the fourth before Dickerson's solo shot to the upper deck off Jordan Zimmermann in the fifth made it 4-2.
LaRoche holds the franchise record for consecutive plate appearances reaching base safely with nine. ... LeMahieu finished with three hits. ... Washington RHP Stephen Strasburg (7-7, 3.55) will face Rockies LHP Jorge De La Rosa (10-6, 4.39) in the series finale on Wednesday.