Bumgarner has been sensational over his winning streak, allowing two earned runs in his last 19 2/3 innings. On Monday against the Los Angeles Dodgers the 20-year-old lefty gave up just two runs (one earned) and six hits in 5 2/3 frames to get the win.
The former 10th overall pick, though, worked just one 1-2-3 inning in the effort.
"He wasn't as sharp tonight. But that's a good sign," Giants catcher Buster Posey said.
Arizona, meanwhile, will pin its hopes on a streaking young hurler of its own in 25-year-old righty Ian Kennedy, who has won his last two starts. Kennedy got a ton of support in beating the New York Mets on Monday, but did not need it, as he surrendered just one run and four hits in five innings.
Kennedy did not get a decision the last time he faced the Giants, but beat them back on May 19, surrendering a run and three hits in eight innings.
San Francisco improved to 4-1 on its current road trip on Friday, as Aubrey Huff hit two home runs and drove in three, as the Giants spoiled Kelly Johnson's cycle and beat the Diamondbacks, 7-4.
Andres Torres added the tie-breaking two-run triple in the seventh inning for the Giants, who took advantage of several Arizona errors to win for the ninth time in its last 11 games overall. San Francisco beat Arizona by a 3-0 score in Thursday's series opener.
Giants starter Jonathan Sanchez got out of several jams to allow only one run. However, the left-hander lasted just five innings, as he threw 109 pitches, gave up four hits, walked five and struck out 10.
Santiago Casilla allowed three runs in the sixth while recording two outs, and Chris Ray (1-0) got the final one to get the win. Brian Wilson recorded the final four outs to earn his 28th save.
Johnson finished 4-for-4 and became the fourth player in team history to hit for the cycle, but it was not enough to keep the Diamondbacks from losing their fifth consecutive game to the Giants.
"Pretty cool thing to say that you did," Johnson said. "But unfortunately we lost."
Edwin Jackson (6-9) took the loss after allowing six runs (four earned) on eight hits and two walks in six-plus innings.
San Francisco leads the 2010 season series with Arizona by a 5-2 margin, and is 18-7 over the past 25 meetings between the two ballclubs.