Bumgarner struck out a season-high 11 over seven innings, Gregor Blanco entered in the fifth as a pinch hitter and drove in four runs, and the San Francisco Giants routed the Atlanta Braves 10-1 Saturday.
"He's nasty," Braves third baseman Chris Johnson said. "For me, he is one of the best lefties in the game. He throws his cutter in to righties. He makes righties feel uneasy."
It was a frustrating day all-around for National League East-leading Atlanta. Dan Uggla struck out four times and Johnson went down three times. After taking Thursday's opener, the Braves have mustered just 10 hits and have been outscored 18-3 in the past two games.
The Giants led 2-1 when they broke open the game with a four-run fifth, aided by Upton's adventures in right field.
Upton let Marco Scutaro's liner skip past him for a one-out triple. After Pablo Sandoval was hit by a pitch, Buster Posey drove an RBI double deep to right that Upton made an awkward attempt on as it bounced up against the wall. Hunter Pence was intentionally walked to load the bases, and Braves interim manager Carlos Tosca called on Cory Gearrin to relieve Paul Maholm (4-4).
Giants manager Bruce Bochy sent up Blanco to hit for Francisco Peguero, and Blanco delivered a three-run double to right-center that extended the Giants' lead to 6-1.
"It is definitely a difficult outfield," Upton said. "You definitely have to make a decision pre-pitch on how aggressive you want to be."
Maholm lasted just 4 1-3 innings and was yielded six runs on eight hits.
Blanco was at it again in the eighth, when the Giants batted around and tacked on four more. His liner to left field skipped past a charging Evan Gattis and went for an RBI triple. Blanco is 9 for 19 this season with runners in scoring position.
Bumgarner is a North Carolina native who grew up rooting for the Braves and had been winless against them in four previous starts. Bumgarner (4-1) gave up just four hits and walked two, winning for the first time since April 13.
San Francisco's rotation, considered one of the best in the majors, has struggled early this season. But ace Matt Cain tossed eight innings of three-hit ball in Friday's win, and coupled with Bumgarner's effort, the Giants can claim the four-game series with a victory in Sunday's finale.
"They've got as good a shot as anybody to play October baseball," Bumgarner said of the Braves. "When you play a team like that, you want to play your best baseball, too."
San Francisco's starting pitchers entered the day with a 4.48 ERA, which ranked 13th out of 15 NL teams. Bumgarner rebounded after his worst outing of the season, when he gave up five runs in six innings against Philadelphia on Monday.
"That's a tough lineup to go through and he did quite a job for us," Bochy said.
Sandoval's homer in the first gave the Giants an early lead. Brandon Crawford doubled in a run in the fourth to make it 2-0, one of two hits the left-handed hitting Crawford had off Maholm. Maholm entered Saturday having surrendered just four hits to lefties all season.
Atlanta scratched out its only run in the fifth, when Gattis doubled and eventually scored on Maholm's opposite-field single to left.