Nationals 2, Cubs 1:
Ross Detwiler tossed seven scoreless innings to outduel Jeff Samardzija and Adam LaRoche blasted his 25th home run as the host Nationals set a Washington franchise record for victories.
The club's 82nd win of the season marks its highest total since moving from Montreal in 2005. The Nationals went 81-81 in their first year in Washington.
The triumph also kept the Nationals 6 1/2 games clear of Atlanta in the National League East.
Detwiler (9-6) limited the Cubs to four hits and three walks to win his second straight start. It's the first time he has won consecutive decisions since April.
Tyler Clippard was unable to preserve the shutout, allowing an RBI single to Welington Castillo in the ninth before striking out Josh Vitters to strand the tying run at second for his 30th save.
Samardzija (8-13) turned in his 16th quality start in 27 outings but suffered another tough-luck loss. He allowed one run on seven hits over seven innings with eight strikeouts.
His only mistake was an 0-1 fastball that LaRoche launched into the second deck in right for a 1-0 lead in the second.
That's where it stood until the eighth, when Bryce Harper led off with a single against Jeff Beliveau and scored from first on Ryan Zimmerman's double down the left-field line.
GAME NOTEBOOK: The Cubs have lost 25 of their last 33 games and are on pace for their worst season since 1981. … Chicago has lost five straight and 14 of 15 on the road and has the majors' second-worst road mark at 17-49. … Zimmerman extended his hitting streak to eight games with his RBI double. … Nationals OF Michael Morse left in the fourth inning with a sore right thumb.