Bumgarner pitched seven strong innings and Buster Posey went 4 for 4 with his 14th homer as the San Francisco Giants topped the Chicago Cubs for a 5-3 victory on Thursday night.
''He's as mentally tough as you get,'' said Giants manager Bruce Bochy about his young pitcher. ''He's got a knack for making pitches when he has to.''
Pablo Sandoval added three hits and two RBIs as the Giants rebounded from a 2-1 loss earlier in the day in the resumption of their suspended game in the series opener.
Bumgarner (14-9) struck out 12 in seven innings. He allowed three runs and seven hits.
Bumgarner finished his strong outing by striking out touted Cubs prospect Javier Baez with two out and two runners in scoring position in the seventh.
''It was a really gutty effort that last inning,'' Bochy said. ''He's our guy, and he got a big strikeout there.''
Baez struck out four times on the night. Through 71 big league at-bats, he has struck out 31 times.
The long day started with a rain delay of 1 hour, 57 minutes, and then the Cubs and Giants played the final 4 1/2 innings of a game the Cubs thought they had won 2-0 on Tuesday night.
A short rainstorm caused a delay of more than 4 1/2 hours after the grounds crew struggled with the tarp. The umpires said the field was unplayable and called it at 1:16 a.m.
But the Giants protested, and Major League Baseball ruled that the tarp had not been properly put away after its previous use. The game was suspended.
''It was a little bit of a strange one with the suspended game today,'' said Bochy, who heavily criticized the initial ruling Tuesday night. ''You know, they got it right.''
It was the first successful protest in MLB since 1986.
Anthony Rizzo's two-run homer from Tuesday held up for Chicago in the early game. Joe Panik had an RBI single in the sixth to pull the Giants to 2-1, but Pedro Strop worked the eighth and Hector Rondon picked up his 19th save in 23 opportunities.
Tuesday's starters proved to be the pitchers of record. Tsuyoshi Wada (3-1) earned the victory for the Cubs, while Ryan Vogelsong (7-9) took the loss.
Chicago then got off to a fast start in the nightcap. Justin Ruggiano and Welington Castillo hit back-to-back homers in the first to give the Cubs a 3-1 lead.
But San Francisco grabbed the lead for good on Posey's leadoff drive to left in the fifth against Travis Wood (7-11). Michael Morse added a sacrifice fly in the seventh that made it 5-3.
''It's been a long three days,'' Cubs manager Rick Renteria said of the series. ''I wished we could have finished it off the second game in our favor, but obviously we didn't.''
Wood (7-11) gave up four runs and eight hits in six innings. The left-hander is 0-6 with a 5.45 ERA in his last 12 starts.
Santiago Casilla worked a scoreless ninth for his 11th save in 14 opportunities.
Cubs: RHP Edwin Jackson was placed on the 15-day disabled list with a right lat strain. Jackson dealt with a similar injury at the end of last season and hopes that by going on the DL now, he will be able to pitch again in September. ... SS Starlin Castro was placed on the bereavement list after leaving the team for a family emergency.
Giants: INF Ehire Adrianza has been slow to recover from a second strained groin injury, which raises doubts about his status in the final weeks of the season. ''He's not ready yet, so that's another decision we'll have to make,'' manager Bruce Bochy said. ... Bochy was optimistic that 1B Brandon Belt and C Hector Sanchez would recover from concussions in time for the stretch drive.
Giants: RHP Tim Hudson (8-9, 3.03 ERA) faces Washington RHP Doug Fister (12-3, 2.20 ERA) as the Giants take on the Nationals on Friday in the opener of a weekend road series.
Cubs: RHP Jake Arrieta (6-4, 2.61 ERA) faces his former club when Baltimore comes to Wrigley Field for a weekend series. RHP Kevin Gausman (7-4, 3.70 ERA) goes for the Orioles.