Jake Arrieta regained his form right after Anthony Rizzo’s towering drive landed in the bleachers in right field.
The unbeaten ace took over from there.
Arrieta struck out 11 in eight innings, Rizzo drove in four runs, and the Cubs remained perfect against the Pittsburgh Pirates with an 8-2 victory on Saturday in Chicago.
Arrieta improved to 18-0 with a microscopic 0.75 ERA in 20 regular-season starts since Aug. 1. The Cubs have won his last 21 starts, extending a franchise record.
‘‘It’s unusual,’’ manager Joe Maddon said with a chuckle. ‘‘It’s very unusual what he is doing.’’
Arrieta (7-0) allowed three hits and two runs, leaving with a major league-best 1.29 ERA. After Rizzo’s 11th homer made it 3-2 in the fourth, Arrieta finished his outing with four hitless innings.
‘‘That was a huge swing of the bat by Anthony,’’ Arrieta said. ‘‘It picked me up.’’
Rizzo also singled in Jason Heyward in the eighth and is among the major league leaders with 33 RBIs. Heyward had three hits and Addison Russell hit a two-run homer.
The 27-8 record for the Cubs is baseball’s best start since the 1984 Tigers went 30-5.
Bouncing back from a so-so start for his lofty standards, Arrieta moved to 8-1 in 11 career regular-season starts against the Pirates. He also struck out 11 in a five-hit shutout at Pittsburgh in last year’s wild-card game.
Francisco Cervelli hit a two-run single for Pittsburgh in the fourth.
The Cubs then grabbed the lead for good in the bottom half. Heyward singled on a dribbler to second and Kris Bryant walked on a full-count pitch before Rizzo connected against Jeff Locke (1-3).
‘‘I got into a little bit of rhythm for a little a while but the Rizzo home run kind of knocked that off course,’’ Locke said.
Yankees 2, White Sox 1 — Dellin Betances, Andrew Miller, and Aroldis Chapman combined for eight strikeouts and 3? scoreless innings of relief, the first time host New York has used its three power bullpen arms all in the same game.
Ivan Nova (2-1) pitched neatly into the sixth inning to give New York’s ailing rotation a much-needed boost. Aaron Hicks hit an RBI double and Didi Gregorius (3 for 3) added a run-scoring single in the second.
That was enough to squeeze past the stingy White Sox (24-13), who began the day with the best record and lowest ERA (3.13) in the American League. Todd Frazier hit his 12th home run for Chicago, which has lost three of four overall — and 11 of the past 14 matchups with New York.
Jose Quintana (5-2) pitched seven strong innings in a hard-luck loss. The lefthander entered leading the AL with a 1.38 ERA that rose to 1.54.
Betances struck out all four batters he faced, Miller fanned two in a one-hit eighth, and Chapman whiffed a pair in a 1-2-3 ninth for his second save.
New York relievers have thrown 15? consecutive scoreless innings.
Orioles 9, Tigers 3 — Jonathan Schoop hit two home runs, including a grand slam, and host Baltimore beat Detroit to stretch its winning streak to seven games.
Miguel Cabrera homered for the Tigers, who have lost 11 of 12.
Matt Wieters and Adam Jones also homered for the Orioles, who will seek to complete a four-game sweep Sunday. Schoop hit a solo shot in the seventh and his second career slam in the eighth to finish with a career-high five RBIs.
Rookie Mike Wright (2-3) gave up two runs and three hits over seven innings. He struck out six and walked three.
Cabrera’s two-run homer in the sixth ended Detroit’s run of 17 straight scoreless innings.
Wieters hit a two-run drive in the sixth inning to put Baltimore up, 3-2, and Schoop’s first home run of the game made it 4-2 in the seventh. Both long balls came off Anibal Sanchez (3-4), who took a two-hit shutout into the sixth.
Nationals, 6-4; Marlins, 7-1 — Marcell Ozuna and J.T. Realmuto each drove in two runs and visiting Miami beat Washington to split a doubleheader. The Nationals won the opener behind six strong innings from Stephen Strasburg.
After the opener, Washington announced that Bryce Harper had dropped his appeal of a one-game suspension and would sit out the nightcap.
Strasburg fanned seven over six innings in his first start since signing a seven-year, $175 million deal last week. He allowed three runs.
The righthander is the first starting pitcher in Nationals/Expos history to start a season 6-0 since Pedro Martinez went 8-0 to begin the 1997 season.
Jayson Werth’s RBI single capped a three-run first inning for Washington off Justin Nicolino (2-1). Wilson Ramos hit a solo home run in the sixth as five Nationals drove in at least one run.
The reigning NL MVP was suspended and fined Wednesday by Major League Baseball.
Rangers 6, Blue Jays 5 — Drew Stubbs homered with two outs in the bottom of the 10th, helping Texas pull out a win after Toronto rallied with consecutive homers in the ninth to force extra innings.
The Blue Jays’ Justin Smoak hit a two-run homer and Troy Tulowitzki followed with a tying shot off closer Shawn Tolleson in the ninth.
Rays 6, Athletics 0 — Matt Andriese (2-0) pitched a two-hitter for his first career shutout as Tampa Bay crused at home.
Dodgers 5, Cardinals 3 — Adrian Gonzalez and Corey Seager homered for host Los Angeles, backing 8? strong innings from Scott Kazmir (3-3).
Phillies 4, Reds 3 — Aaron Nola (3-2) tied a career high with nine strikeouts, and Philadelphia held on at home when left fielder Tyler Goeddel threw out Eugenio Suarez at the plate to end the game.
Giants 5, Diamondbacks 3 — Buster Posey hit a two-run double in the ninth and Hunter Pence had his 200th career home run to power San Francisco in Phoenix.
Rockies 7, Mets 4 — At Denver, DJ LeMahieu and Tony Wolters had two RBIs apiece to pace Colorado.
Twins 6, Indians 3 — Ervin Santana (1-2) allowed one run in six innings, and visiting Minnesota ended an eight-game losing streak.
Padres 8, Brewers 7 — Visiting San Diego got 12th-inning homers from Derek Norris and Melvin Upton.
Braves 5, Royals 0 — Kelly Johnson and A.J. Pierzynski each drove in two runs, and Mike Foltynewicz (1-1) pitched a career-high eight scoreless innings to lead visiting Atlanta.
