All games on WGN-AM 720.
Season series: Tied 2-2.
Friday: 10:05 a.m., WGN-9.
RH Jason Hammel (7-5, 2.98) vs. RH Tanner Roark (7-5, 2.98).
Saturday: 3:05 p.m., CSN.
RH Jeff Samardzija (2-7, 2.83) vs. LH Gio Gonzalez (5-4, 3.93).
Saturday: 12:35 p.m., WGN-9.
RH Jake Arrieta (5-1, 1.81) vs. RH Jordan Zimmerman (6-4, 2.95).
Who's hot: Hammel has averaged 10.10 strikeouts over his last six starts and has a 7-0 lifetime record against the Nationals. Arrieta was 4-0 with a 0.92 ERA in June. The Nationals have won five consecutive games. Right fielder Jayson Werth is 5-for-7 with one home run and five RBIs.
Who's not: Cubs outfielder Junior Lake is 0-for-15 with six consecutive strikeouts. Catcher Welington Castillo is 1-for-10. Nationals center fielder Denard Span is 2-for-10. First baseman Adam LaRoche is 2-for-11.