PHILADELPHIA -- Jake Arrieta pitched eight strong innings to run his personal winning streak to eight games as the Chicago Cubs beat the Philadelphia Phillies 5-1 in the opener of a double-header on Friday night.

Arrieta (19-6) allowed one run and six hits, while striking out seven and walking two. He leads the major leagues in victories, and is the first Cubs pitcher to win 19 games since Jon Lieber went 20-6 in 2001.

Arrieta's winning streak is the longest by a Cubs pitcher since Milt Pappas won 11 straight in 1972. He has not dropped a game since the Phillies beat him 5-0 on July 25, when the Cubs were no-hit by Cole Hamels.

Second baseman Starlin Castro hit a solo homer and shortstop Addison Russell had a two-run double for the Cubs, who won for the sixth time in seven games.

Right fielder Aaron Altherr hit a solo homer for the Phillies, who lost for the sixth time in seven games, and the 13th time in 17.

Altherr's homer, his third in 20 games with the Phillies, came with two outs in the second, on a 2-0 slider from Arrieta.

The Phillies also put two men aboard in the third and fourth, but could not score.

Chicago took a 2-1 lead on consecutive two-out RBI doubles by right fielder Austin Jackson and left fielder Kris Bryant in the fifth. Both came off Philadelphia starter Adam Morgan (5-6).

Castro and third baseman Javier Baez opened the sixth with singles, knocking Morgan out of the game. Both runners scored on Russell's one-out double to left off reliever Hector Neris.

Castro hit Neris' 1-1 slider into the seats in right with two outs in the seventh, extending the Cubs' lead to 5-1.

Castro, Baez, Bryant and center fielder Dexter Fowler all had two hits for Chicago.

Morgan went five innings and allowed four runs and seven hits, while striking out five and walking one.

Justin Grimm pitched a scoreless ninth for the Cubs.

NOTES: The Phillies played their second "traditional" double-header -- i.e., the second game starting approximately 30 minutes after the first -- of the season. Before this year, they had not played one since 2009. It was the first such double-header for the Cubs since 2006. ... It was also the first twin bill between the Phillies and Cubs since 2001 at Wrigley Field, and the first between the two teams in Philadelphia since 1990.