OAKLAND -- Brandon Belt did not like the last pitch. The outside fastball struck him out looking and ended the game. He gave home-plate umpire Mark Carlson a mouthful about the call as the Giants coaches monitored carefully from the dugout and Grant Balfour walked off the mound toward his catcher.
Belt shouted. Balfour nodded.
"I liked it," Balfour said. "Hitters don't like it when they get punched out. Pitchers don't like it when they walk guys."
Neither the A's nor the Giants like losing to each other, and on Monday the loud sold-out Oakland Coliseum crowd with fans of both teams witnessed the A's win the first game, 4-1, of a four-game home-and-home Interleague series against the Giants (28-23).
It is the only regular-season meeting scheduled between the Bay Area teams.
The A's (29-23) put matchups against the defending World Series champion Giants in playoff-like context, which explains the atmosphere and exchanges of "Let's go A's! ... Let's go Giants!" cheers and why Josh Donaldson smacked his hands as his two-run home run off Giants starter Madison Bumgarner (4-3, 3.13 ERA) landed over the right-center wall in the fourth inning, giving the A's a 2-0 lead.
"I'm big into rivalries and stuff, so it was fun," Donaldson said.
Added Bumgarner: ""I tried to throw the fastball down and away. It came back over the plate a little bit but it was down. He just put a good swing on it. I couldn't put it exactly where I wanted."
Donaldson's shot and a two-run double by Yoenis Cespedes in the seventh backed Dan Straily's second straight solid start and a scoreless bullpen effort capped by Balfour's 11th save of the season in as many opportunities.
Straily (3-2, 5.08 ERA) got the hook after 78 pitches (52 strikes), all it took him to work six quality innings. He allowed four hits, one walk and a run off Buster Posey's groundout in the sixth.
The outing gave Straily back-to-back quality starts, following his best career outing against Texas on Tuesday, when he tossed seven shutout innings. On Monday, he worked fast, filled up the strike zone and, he said, was "excited about every quality pitch."
"You can see, early innings, you can tell he's got a lot more confidence, the way he's carrying himself," Oakland manager Bob Melvin said. "He's throwing a lot of strikes, which is key for him to get ahead to set up his slider and his changeup. His fastball has been really good. You see a lot of late swings on his fastball, and that all starts by getting ahead."
Reliever Sean Doolittle (0.78 ERA) continued his dominance by working a perfect seventh and eighth innings with two strikeouts before Balfour (1.33 ERA) converted his 29th consecutive save opportunity dating back to last season.
The A's got four hits and drew five walks on Giants starter Madison Bumgarner, San Francisco's best pitcher this season. He threw 100 pitches through six innings but stayed in, leaving after his 115th pitch with runners on first and second and two outs in the seventh and Oakland ahead, 2-1. George Kontos entered to face Cespedes, who clubbed a two-run double off the right-center wall, both runs attributed to Bumgarner.
Cespedes went 1-for-3, his double tying his career-high hitting streak of nine games. It also provided a cushion on an afternoon when Straily actually had his lowest pitch count of the season and could have gone longer, but at the time the 2-1 lead gave way to a bullpen that is excelling.
"We just have this knack for winning the close ones," Straily said. "Then again, if you had this bullpen, you probably would, too."
Balfour's ninth included a walk of Posey, whose at-bat contained its own borderline call. Posey was on second when Belt struck out on the full count.
After the strikeout, A's fans roared. Melvin and the A's do not like sending their big crowds home unsatisfied.
"This is a little different in this series when you get that type of crowd because it almost feels a little split at times," Melvin said. "It's just a different feeling. You don't have to get up for these games. You don't have to find extra adrenaline. We came from a four-hour flight yesterday, we have a day game today, guys are ready to play. And that's the reason why our fans get after it a little bit. It's just got a different feel to it, these games."
Willie Bans is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.