Washington, DC (Sports Network) - Starlin Castro hit a go-ahead double in the eighth and Aramis Ramirez added a two-run blast later in the inning, as Chicago completed a three-game sweep of Washington with a 4-0 victory.
The rally in the eighth made a winner of Ryan Dempster (12-8), who threw seven innings of two-hit ball to go with eight strikeouts and one walk.
Washington's Jason Marquis (0-7) was also effective but took the loss after getting charged with one run on four hits and three walks in 7 1/3 innings.
Both starters were stingy with baserunners throughout the night until Marquis walked pinch-hitter Tyler Colvin leading off the eighth.
Marquis was pulled after getting Kosuke Fukudome on a flyout, and Colvin stole second with Castro at the plate. Castro followed with a run-scoring double to the left-field corner off Tyler Clippard, who later served up Ramirez's two- run blast to left on a 1-2 pitch.
Andrew Cashner stranded a runner on second in the bottom half, and Alfonso Soriano added his 21st homer to open the ninth to account for the final margin.
Nationals outfielder Nyjer Morgan appealed a seven-game suspension for throwing a ball into the stands that hit a fan at Philadelphia's Citizens Bank Park last weekend and went 0-for-3...The Cubs have won seven straight at Nationals Park and won consecutive road series for the first time this year..Mike Quade, serving as interim manager, became the first Cubs skipper to win his first three games at the helm since Jim Riggleman in 1995. Chicago had lost six of its final seven games with Lou Piniella at the helm...Dempster, who moved to 8-1 lifetime against Washington, is unbeaten (4-0) in five August starts.