"Curveball was as good as it's been all year," Arrieta said. "I was able to throw it in the middle [of the plate], but underneath the zone, at will for the most part to give the appearance of a belt-high fastball."
In the sixth inning, Arrieta needed a Houdini act to escape with the lead.
After a strikeout of Tyler Moore, Denard Span singled and Anthony Rendon doubled to right -- Junior Lake misplayed a soft line drive, making two bases possible. Danny Espinosa was hit by a pitch to load the bases and bring Bryce Harper to the plate.
"You've got to reset the mind every pitch," Arrieta said. "So that doesn't change there, mentally."
Harper notched his 45th RBI of 2015 -- and the first Nationals run in 18 innings -- but Arrieta won the battle, inducing a chopper to Starlin Castro at shortstop for the second out. Arrieta proved a bit wild once more by hitting Ryan Zimmerman, but when first baseman Anthony Rizzo was perfectly positioned to field an Ian Desmond line drive, the inning was over with the Cubs in front, 2-1.