SAN FRANCISCO -- After watching their teammates strike out 14 times against San Francisco Giants ace Madison Bumgarner, San Diego Padres reserves Will Venable and Alexi Amarista knew they still could help provide a happy ending Tuesday night.

And that they did.

Venable rallied the Padres from a 2-0 deficit in the eighth inning with a two-run double, and Amarista produced a tiebreaking single in the 11th, lifting San Diego to a 3-2 victory in the opener of a three-game series.

In winning for just the third time in nine games, the Padres came off the mat against Bumgarner, who recorded a career-best 14 strikeouts.

"This is my first go-round," Padres manager Pat Murphy joked afterward. "That guy's had some success?"

It was no laughing matter when Murphy was ejected in the eighth inning with his team down two runs to the reigning World Series Most Valuable Player.

Two pitches later, Venable, who entered the game as a defensive replacement in the sixth inning, tied the game with his double.

"A lot of people did a lot of good things for us today," Venable said. "That's how we have to play."

The loss denied the Giants (38-34) a chance to move into a first-place tie with the Los Angeles Dodgers (39-33) in the National League West.

Catcher Derek Norris triggered the game-winning uprising against right-hander Hunter Strickland (0-1), the sixth Giants pitcher, with a one-out double in the 11th.

Norris advanced to third on a single by left fielder Justin Upton, then raced home when Amarista's potential double-play grounder up the middle deflected off Strickland's glove and into short right field.

"Felt great," Murphy said of the first major league victory of his career that he was able to watch from the clubhouse. "The guys battled the way they did. The pitching was great all game. Team win.

"Some luck ... we needed some of that."

Right-hander Brandon Maurer (5-0), the fifth Padres pitcher, got the win after holding the Giants hitless in the ninth and 10th innings. Closer Craig Kimbrel pitched around a one-out walk in the 11th for his 18th save, sealing San Diego's fifth win in eight meetings with the defending World Series champs this season.

"We're trying to build some kind of streak," Venable said. "To do that, we just have to go out and play a good ballgame. That's what we're thinking right now."

The Giants' 10th loss in their past 11 home games was decided well after Bumgarner was pulled from a 2-2 tie.

"Tough one to lose," San Francisco manager Bruce Bochy said. "Bum threw so well again. We've got to find a way to get this offense clicking."

Bumgarner took a three-hit shutout into the eighth inning, but the Padres denied the Giants ace a win with an uprising that was interrupted by two ejections.

Venable's two-run double was the big hit of the inning, scoring first baseman Yonder Alonso and third baseman Will Middlebrooks and ending Bumgarner's night. It was just the left-handed-hitting Venable's fifth hit all season against a lefty pitcher.

The hit came after Murphy got thrown out for the first time in his career for arguing a check-swing strike call with plate umpire Fieldin Culbreth. San Diego right fielder Matt Kemp also got ejected when he got into it with first base umpire Jim Reynolds, who hadn't participated in the call.

"Did it work? Then it was tactical," Murphy said of the ejection, which caused a delay while Bumgarner cooled off on the mound. "You try to support your players. If it looked like (I was intentionally delaying the game), so be it."

Trying to get a six-game Giants homestand off to a successful start, Bumgarner got a no-decision. He allowed the two runs on five hits in 7 1/3 innings.

His 14 strikeouts, nine of which came in the first four innings, were one better than his previous career high, set twice, including once against the Padres on Sept. 5, 2011.

"I don't care if I strike a lot of guys out," Bumgarner said. "Today was just like that."

He walked just one, Alonso, to open the fateful eighth.

Padres starter Odrisamer Despaigne also did not factor in the decision despite a strong effort.

The Giants nemesis, who allowed only one earned run in his previous 24 2/3 innings against San Francisco, was pulled after five innings, having allowed two runs on five hits. He walked two and struck out two.

Middlebrooks had two of San Diego's eight hits. The Padres out-hit the Giants 8-7.

The Giants' runs against Despaigne came in the fifth, an inning that featured doubles by third baseman Matt Duffy and second baseman Joe Panik.

Left fielder Gregor Blanco, moved up to the leadoff spot in a lineup change made shortly before game time, had two hits, two walks and an RBI to lead the Giants' attack.

NOTES: The Giants announced after the game that LF Nori Aoki, who had been in their initial starting lineup, was diagnosed in the early evening with a fractured lower right leg. He will be placed on the disabled list Wednesday. ... The Giants experienced another setback when RHP Sergio Romo had to be removed from the game in the ninth inning with a sprained left ankle. ... The Giants activated RHP Jean Machi (strained left groin) from the 15-day disabled list before the game and sent RHP Mike Broadway to Triple-A Sacramento. ... Giants LHP Madison Bumgarner struck out 10 or more for the 22nd time in his career. His 14 strikeouts tied the Giants' West Coast record for a left-hander, equally a feat achieved previously by Atlee Hammaker. ... The come-from-behind win was the Padres' 17th of the season.