"They were saying they don't think that can happen," manager Bruce Bochy said.
Moments later, however, a raucous cheer from the bowels of the clubhouse signaled that the celebration was on.
For eight innings, Bumgarner was on, too.
Making his third start since being summoned from Triple-A Fresno, Bumgarner blanked Milwaukee on three singles, only one of which went untouched by an infielder. He permitted just two Brewers to reach scoring position and retired 18 of the final 21 hitters he faced, demonstrating why the Giants selected him in the first round (10th overall) in the 2007 First-Year Player Draft.
"It's a very humbling experience, to get a win up here. It's the best there is," said Bumgarner, who at 20 years and 340 days became the youngest Giants starter to record a victory since Matt Cain beat Arizona on Sept. 4, 2005. Cain was 20 years and 338 days old at the time of his milestone.
Bumgarner -- who sipped a sports beverage after the game, not beer -- broke his pattern of struggling in the early innings. In his first Giants start, he yielded two homers and four runs to Boston in the first two innings. Last Thursday at Colorado, he served up Carlos Gonzalez's two-run, first-inning homer.
As the clubhouse began smelling more like a fraternity house due to all the spilled beer, Bumgarner said that he "really didn't think about" the possibility of more instant adversity, though the Brewers rank second in the National League in scoring and home runs.
Bumgarner issued a pair of one-out walks in the second inning before coaxing George Kottaras' fielder's-choice grounder and striking out opposing pitcher Randy Wolf. Milwaukee again had runners on first and second with one out in the third, but Bumgarner responded by striking out All-Star left fielder Ryan Braun and retiring Casey McGehee on a bloop to first base.
After that, Bumgarner went virtually unchallenged.
"That's as good as I've seen him, I think," said Buster Posey, who has caught Bumgarner since last year. "He threw the ball in and out really well. He had that cutter working and was able to throw the changeup for a strike when he needed it. Later in the game, he started flipping curveballs the third and fourth time through the lineup."
Wolf, a 12-year veteran, offered sincere praise for Bumgarner.
"I couldn't pick up the ball off him, that's for sure," said Wolf, who entered the game batting .289 but struck out twice. "He kind of has a little bit of a hitch in his delivery and steps across his body. I know as a left-handed hitter, it's hard because with his arm angle and where he strides, you feel like the ball is coming from behind you. He hides the ball well. He's obviously a highly touted prospect and has good stuff."
Wolf (6-8) was equally effective as five scoreless innings unfolded. But the Giants broke the tie with five runs in the sixth inning, primarily because Milwaukee's defense committed an egregious mistake for the second game in a row.
Shortstop Craig Counsell, the typically reliable 14-year veteran, committed a throwing error after fielding Pablo Sandoval's sixth-inning grounder, which seemed certain to result in an inning-ending double play. Two runs scored as Counsell's relay flew wide of second base and into right field. Travis Ishikawa followed with a two-out, two-run single. Bumgarner, whose hitting skills outclass those of most pitchers, then singled to right for his first big league RBI.
On Monday, rookie shortstop Alcides Escobar botched a potential double-play grounder to help the Giants score four seventh-inning runs. Ironically, Counsell was in Tuesday's lineup to give Escobar some mental relief.
Ishikawa knows the heartache of committing an error that generates an opponent's big inning.
"You feel like the bottom of the bottom," he said. "You just kind of want to hide. When that happens to me, I want the next ball to come to me so I can help make up for it. But when runs score, you just feel terrible. You want to apologize to the pitcher. But you know he's upset, too."
Of course, the Giants weren't upset at all -- especially since San Diego lost, trimming their deficit in the NL West to six games.
"We got a break. We know it," Bochy said. "But you have to take advantage of them, too."