Dexter Fowler and Anthony Rizzo keyed a two-run rally in the fifth inning that gave Hammel a 3-1 cushion to work with. After Jonathan Herrera's RBI single gave Chicago a 4-1 lead in the ninth, Bryce Harper led off the home half of the ninth with a home run.
The Cubs improved to 29-25, while the Nationals dropped into a first-place tie with the Mets (30-26), pending the outcome of New York's game with Arizona.
MOMENTS THAT MATTERED
Ross on the mound: Ross became the sixth Nationals pitcher to make his big league debut this year.