Bryant launched his 11th homer with two outs in the first, and Heyward and Zobrist led off the fifth and sixth innings, respectively, to hand the Giants their 12th loss in the past 14 games at Wrigley Field, which includes postseason play. Chicago now has 26 home runs in the past 14 games, second-most in the National League behind the D-backs (28).
"We have that kind of power on our team," manager Joe Maddon said of the Cubs, who finished the 7-2 homestand with 20 homers. "We needed to get into our groove a little bit. It is a part of our game."
Said Cubs starter Eddie Butler: "Long balls are fun, and they're contagious. Guys are really swinging it well right now and having fun."
All three homers came off Samardzija, who was facing his former team for the first time since losing Game 2 of the NL Division Series in October at Wrigley Field. The right-hander, drafted by the Cubs and on the team from 2008-14, struck out eight over seven innings.
"Facing a lineup like theirs, you have to be 'on' the whole time," Samardzija said.
Besides taking the loss, Samardzija also walked rookie Ian Happ with two outs in the sixth; he had gone 154 batters since the last free pass he issued.
"We were throwing him fastballs," said Samardzija, who worked the count to 3-2, "and just missed a little bit."
Butler picked up the win, and he improved to 4-0 in his career against the Giants. He's 4-16 with a 6.72 ERA against all other teams. San Francisco's only run came in the first when Denard Span doubled to lead off and scored one out later on Brandon Belt's double.
The Cubs took advantage of sloppy play in the eighth to add two more runs. Chicago loaded the bases against Josh Osich, and his first pitch to Heyward skipped in the dirt for a wild pitch. One run scored, and then another on catcher Buster Posey's throwing error.
Mike Montgomery notched a four-inning save for the Cubs, holding the Giants scoreless and yielding only one hit.
MOMENTS THAT MATTERED
Bleacher creatures: Bryant may have gotten a little help from a fan in the bleachers. He launched the first pitch from Samardzija to left, and a fan reached out and snagged the ball with his glove. Giants left fielder Mac Williamson seemed to indicate the fan interfered, but manager Bruce Bochy did not challenge the call, though the team's review crew telephoned him to request an examination of replays. However, the phone did not ring in the Giants' dugout.
"It was ironic that as soon as that came up, the phones stopped working," said Bochy, who defused controversy by agreeing that Bryant's homer was legitimate.
Said Maddon about the fan: "I think it's almost impossible to reach that far."
Say Hey: All the work Heyward put into his swing in the offseason has paid off. He hit four homers in 79 games in the first half of 2016, and he is well ahead of that pace with his fifth on Thursday (he didn't hit his fifth in '16 until July 29). According to Statcast™, his home run had an exit velocity of 108 mph and traveled 373 feet, landing in the basket rimming the right-field bleachers. On Wednesday, the wind blew a potential homer foul; it wasn't a factor this time.
"He looks very confident," Maddon said of Heyward. "He's playing at the top of his game right now."
With one out in the Giants' fifth, Butler threw to first baseman Anthony Rizzo in attempt to pick off Span. Span was called safe by first base umpire Doug Eddings, but the Cubs challenged the ruling. After a review, the call was overturned and Span was out. Butler got Joe Panik to ground out and end the inning, which was key for the Cubs, Maddon said.
"I'll tell you what was big was the pickoff," Maddon said. "That set it all up -- that permitted Panik to make the last out. The tipping point for us in that game was the pickoff at first base."
The Cubs' defense shined. Happ made two stellar catches, robbing Span of a hit for the second out in the third, and grabbing Posey's fly ball on the run for the second out of the sixth. In the eighth, shortstop Javier Baez threw out Panik from shallow left, and his throw was clocked at 84.1 mph, the 10th-hardest throw to first by a shortstop that Statcast™ has tracked this season.
"That play, after I caught the ball, I had pretty good balance, and I felt like I made a strong throw, really strong," Baez said.
WHAT'S NEXT Giants: The Braves come to AT&T Park, where the Giants own an 11-10 record, to open a three-game series on Friday at 7:15 p.m. PT on MLB.TV. This date will also launch a six-game homestand for San Francisco, which will give the ball to Matt Cain in the opener. Cain has not faced Atlanta since 2015.
Cubs:Jake Arrieta will open the Cubs' West Coast road trip on Friday, pitching at one of his favorite ballparks, Dodger Stadium. Arrieta threw his first career no-hitter there on Aug. 30, 2015, against the Dodgers. In his most recent outing, the right-hander gave up one unearned run over six innings. First pitch will be 9:10 p.m. CT on MLB.TV.