After Buster Posey caught Altuve trying to steal third in the first, Bumgarner whiffed Carlos Correa and Evan Gattis. He set down Jed Lowrie, Chris Carter and Hank Conger via the strikeout in the second and then finished off the feat fanning Jake Marisnick and Scott Kazmir in the third.
Posey said he wasn't even aware of the streak until reporters informed him after the game.
"I didn't even know it, to be honest with you, until just now," Posey said. "But it was fun."
Bumgarner had all of his pitches working. He punched out six Astros with sliders, four via curveballs and two on fastballs.
"He was getting ahead of hitters and then he's able to finish them off," Posey said. "[When] he's got that good curveball going, it makes the fastball, cutter, slider even more difficult."
The Astros offense, which arrived at AT&T Park second in the Major Leagues in total strikeouts, did not have it any easier facing the reigning World Series Most Valuable Player.
Bumgarner finished the night with 12 strikeouts, two shy of the career high he set June 12 against Arizona. Tuesday's dominant outing was the lefty's fourth double-digit strikeout performance of the season and the 23rd of his career.
"I think we definitely kind of expect [Bumgarner] to go out there and do that every day, but it's still always impressive," Brandon Belt said. "Just being able to watch him day in and day out, it's pretty special to see a talent like him. He's the guy that we all feel like when he's out there, we're going to win the ballgame."