Jul 23, 1:50 AM EDT

Arenado, Dickerson homer but bullpen falters as Rockies falls to Nationals, 7-4.

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DENVER (AP) -- The Colorado Rockies showed plenty of power early. Their bullpen couldn't make it stand up.

Nolan Arenado and Corey Dickerson homered to give Colorado a quick lead but Washington rallied late to beat the Rockies, 7-4, on Tuesday night.

DJ LeMahieu had three hits for Colorado, which lost its seventh straight and remain tied with Texas for the worst record in the majors.

"We had a nice game early," manager Walt Weiss said. "We didn't put the game away. We need to play a complete game to win."

Adam LaRoche hit a tiebreaking home run in the seventh and Anthony Rendon had three hits for Washington. 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 loss was just one setback for the Rockies on Tuesday. Before the game the Rockies placed shortstop Troy Tulowitzki on the 15-day disabled list with a left hip flexor strain and recalled left-hander Yohan Flande.

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.

Tulowitzki said his leg injury is an aftereffect of the torn quadriceps tendon he suffered in 2008.

"That `08 injury really put me behind the eight-ball because when you completely tear a muscle, it never gets the same again," he said. "All the other muscles have to help support. I knew it was going to be a long road back from that injury. I didn't know to the extent but here we are six years later and it's still giving me issues."

Even with the major league's leading hitter on the shelf Colorado was in a position to win.

The Rockies took a 1-0 lead in the second on 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 in the fifth made it 4-2.

"He kept throwing in on me, he left a pitch out over the middle of the plate and I got a good swing on it," Dickerson said.

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.

Ryan Zimmerman made it 4-3 with a fielder's choice but left the game with a strained right hamstring after hitting the first base bag hard trying to beat out his grounder.

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. Rex 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.

"It was supposed to be a fastball down and away," Brothers said. "I threw it on the inner third."

Reliever Craig Stammen (1-4) pitched a scoreless inning to get the win. Rafael Soriano worked the ninth for his 23rd save.

Nationals starter Jordan Zimmermann allowed four runs on eight hits and struck out six in five innings. He has just one win since June 8.

NOTES: 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.

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