Bumgarner, San Francisco's Opening Night starter, has not fit the profile of an ace. Rene Rivera drove in all of San Diego's runs in a two-inning span off Bumgarner (2-3), whose ERA climbed to 3.74. The All-Star left-hander's effectiveness hasn't completely deserted him, as his 37 strikeouts in 33 2/3 innings illustrate. But he also has surrendered 45 hits while looking much more vulnerable than dominant.
Moreover, Bumgarner hasn't benefited from AT&T Park's pitcher-friendly traits. He's 1-3 with a 6.20 ERA in four home starts.
"I was a little off," Bumgarner said. "I have to figure out what it was and work on it, get it fixed before my next start. My command obviously wasn't very good."
Giants manager Bruce Bochy remained respectful toward Bumgarner by saying, "We're pretty spoiled with Madison." Yet Bochy refrained from making any excuses for him.
"I think it's fair to say that he made a few more mistakes than we're accustomed to," Bochy said.
An ample number of those mistakes were seized upon by Rivera, who established a personal best for RBIs. He drilled a two-run double in the fourth inning, added a three-run homer in the fifth and became the 11th catcher in Padres history to record five or more RBIs in a game.
"We had a pretty good game plan going in today, I think," Bumgarner said. "I just wasn't able to make pitches. I left a lot of balls out over the middle."
The Padres capitalized on enough of those lapses, despite being the National League's lowest-scoring team.
"He was in and out of the zone early in the game and our guys did a good job of laying off some borderline pitches," Padres manager Bud Black said. "We fouled some balls off, we took balls and for the most part swung at strikes."
Especially Rivera, who achieved the highest RBI total by any Padre in a game at AT&T Park.
"We needed a game like that from one of our guys," Black said. "It's been a long time coming for us. We've had some difficulty scoring runs."
Rivera's homer erased a 3-2 Giants lead that they grabbed in the fourth inning against San Diego starter Tyson Ross (3-3), whose 12-inning scoreless streak against the Giants ended. Angel Pagan singled and scored on Hunter Pence's triple. After Belt walked and advanced on a wild pitch, Michael Morse singled home both runners.
Brandon Hicks led off the Giants' fifth inning against Ross with his second homer in two days to trim San Diego's lead to one run. After Javier Lopez allowed a ninth-inning run to cap San Diego's scoring, Huston Street pitched a 1-2-3 inning to improve to 10-for-10 in converting saves.
San Francisco's offense remained imbalanced. Morse collected a season-high three hits and hiked his team-high RBI total to 19. Buster Posey added two hits, including a sixth-inning double that would have been a homer with just another few feet of altitude.
Belt improved upon Sunday's four-strikeout performance by putting the ball in play twice, but struck out once. Sandoval went 0-for-4 after a promising two-hit afternoon Sunday as his batting average dropped to .172.
"It's a work in progress," Bochy said, referring to Belt and Sandoval. "Our corner guys are going to have to get going for us to have success and put runs on the board."