Nationals 5, Astros 0: Jordan Zimmermann won his sixth straight decision, matching a career high with 11 strikeouts over six shutout innings as red-hot Washington completed a four-game sweep at Houston.

Michael Morse extended his career-best hitting streak to 18 games, homering twice and finishing with three RBIs as the Nationals won their sixth straight game. It was also Washington's sixth consecutive road win and 10th in its previous 11 games away from the nation's capital.

Washington (69-43), which has the best record in baseball, increased its lead to 4 1/2 games over Atlanta in the National League East.

The Astros (36-77), the worst team in the majors, have lost five straight and are 4-34 in their last 38 games.

Zimmermann (9-6), whose 2.35 ERA is third in the majors and second in the NL, has not lost since June 22 and has a 1.47 ERA in nine starts during that span. He allowed three hits and didn't walk a batter.

Lucas Harrell (9-8), who had won his last two starts - Houston's only two victories in the past 22 games - fell to 6-2 at home. He yielded two runs, five hits and struck out five in five innings.

The Nationals scored twice in the fifth inning. Roger Bernadina led off with a single, stole second and scored on Adam LaRoche's bloop single following a Ryan Zimmerman walk. Morse followed with a sacrifice fly to plate Zimmerman.

The Astros escaped further damage in the fifth when Justin Maxwell climbed the hill in center field to make an over-the-shoulder catch, taking extra bases away from Jayson Werth with one on. Harrell retired Zimmermann on a lineout to center with the bases loaded to end the inning.

Morse greeted reliever Mickey Storey with a no-doubt blast to left field in the sixth inning and took Fernando Rodriguez to the opposite field in right in the eighth for his 10th of the season.

GAME NOTEBOOK: Nationals rookie OF Bryce Harper, who was 0-for-11 in the first three games of the series, did not play. ... Zimmermann struck out 11 against Atlanta on May 12, 2011. ... Washington improved to 19-8 against NL Central teams. ... The Nationals swept the Astros in a four-game series for the first time and recorded a sweep in a series of at least three games over Houston for the first time in 12 years. ... Harrell has allowed two earned runs or fewer in six straight starts and eight of his last nine. ... Bernadina had three of Washington's 12 hits and stole two bases. ... Brett Wallace had three hits for Houston. ... The Nationals won the season series 6-2. ... Los Angeles Angels ace Jered Weaver leads the majors with a 2.13 ERA while San Francisco's Ryan Vogelsong is second at 2.27.