PHILADELPHIA -- Jake Arrieta didn't feel on top of his game. He still displayed dominance that has him among the leading NL Cy Young Award candidates.
Arrieta pitched eight strong innings for his major league-leading 19th win, and Starlin Castro homered to lead the Chicago Cubs past the Philadelphia Phillies 5-1 in the first game of a doubleheader Friday night.
In the second game, Kyle Schwarber homered twice to lead the Cubs to a 7-3 win and a sweep of the doubleheader.
Arrieta said his timing was off, but it didn't prohibit him from shutting down the Phillies.
"Sometimes your body reacts differently on certain nights and it's hard to get into that rhythm," he said. "The adjustment necessary to have a quality outing can be made regardless of how you feel."
Arrieta (19-6) won his eighth straight start, allowing six hits with seven strikeouts and two walks to become the first Cubs pitcher to win that many in a row since Milt Pappas won 11 consecutive games in 1972. In his last 16 starts dating to June 21, the right-hander is 13-1 with a 1.00 ERA and 115 strikeouts in 117 innings. He lowered his season ERA to 1.99.
"Nothing fazes me," Arrieta said. "Men on base, walks, homers. ... Deal with it and move forward."
While Arrieta deflected questions about possible upcoming milestones, manager Joe Maddon didn't back away from Cy Young talk.
"I definitely believe our guy deserves it, no question," Maddon said. "I've seen (Zack) Greinke pitch. I know he's really good. I'm getting to watch Jake in person; it's pretty spectacular to watch. My vote's for Jake."
Addison Russell hit a two-run double and Kris Bryant set a club rookie record in the opener with his 87th RBI for Chicago, which entered play nine games ahead of San Francisco for the second NL wild-card spot. The Cubs have won seven of their last eight.
Bryant homered, had three hits and drove in three runs in the nightcap to up his RBI total to 90. He leads all major league rookies in the category.
Aaron Altherr homered in the first game for Philadelphia, which has lost 14 of 18. Ryan Howard snapped a 0-for-35 skid, the worst slump of his career, with a seventh-inning double in the second game.
"That was nice to see," Phillies interim manager Pete Mackanin said of Howard snapping the skid. "It happens to the best of them. We're just hoping he's going to get hot again."
The nightcap was necessitated by Thursday night's rainout.
The only blemish for Arrieta was Altherr's second-inning solo homer, which halted his streak of consecutive innings without an earned run at 30 2/3.
Adam Morgan (5-6) allowed four runs and seven hits in five-plus innings.
"I got some balls over the plate and they're a good-hitting team," Morgan said.
The Cubs went ahead with two two-out runs in the fifth. Dexter Fowler tied the game at 1 when he scored from first on Austin Jackson's double to left, and Jackson reached on Bryant's double to right.
Philadelphia played its first game since Thursday's firing of general manager Ruben Amaro Jr.
In the second game, Kyle Hendricks (7-6) gave up three runs and four hits in 6 2/3 innings to earn the win in his first-ever start against Philadelphia.
Alec Asher (0-3), making his third start since the Phillies acquired him in the trade that sent Cole Hamels to Texas, allowed six runs and seven hits in five innings. Asher has allowed 17 earned runs in 14 1/3 innings.
Hector Rendon relieved Fernando Rodney with two on and no outs in the ninth and got his 28th save in 32 chances.
The win keeps the Cubs in excellent shape to make the playoffs for the first time since 2008.
"Everybody's thinking about October," Hendricks said. "We can smell it."
Bryant eclipsed Billy Williams (1961) and Geovany Soto (2008), who each had 86 RBIs as rookies.
"It just shows, when there's people on base he becomes an even better hitter," Maddon said. "You get guys with that mentality, it makes all the difference in the world."
Castro, who lost his role as an everyday player to 21-year-old shortstop Russell, belted his eighth homer with two outs in the seventh. It was the 13th RBI in 17 games in Philadelphia for Castro, who is 9 for 16 in his last five games overall. He rested in the nightcap.
Phillies: Mackanin said 3B Maikel Franco (fractured left wrist) will take live batting practice "in a few days." Mackanin is eyeing Sept. 22 at Miami as a possibility for Franco, who has been on the DL since Aug. 12, to rejoin the club.
RHP Dan Haren (9-9, 3.73) takes the mound for the Cubs on Saturday night against Phillies RHP Jerad Eickhoff (1-3, 4.70).