SAN FRANCISCO -- The night seemed to bode well for the Giants after Kevin Pillar delivered their first grand slam in two years, helping to turn a five-run lead over to ace Madison Bumgarner.

But the big hit would end up squandered, as the Padres came back to score six unanswered runs and stun the Giants, 6-5, in Monday night’s series opener at Oracle Park.

“We expect to win that game,” manager Bruce Bochy said. “That’s one of those tough ones. You’re going to have to deal with some of these games. It’s going to happen. You hate to see it, especially where we’re at in trying to get some wins. So that’s what makes it tough. We just made some mistakes and had trouble keeping the ball in the ballpark tonight.”

Bumgarner took the mound in the seventh inning looking to protect a two-run lead, but he hit Fernando Tatis Jr. to put the leadoff man on board for the Padres. Bochy came out for a mound visit, but he opted to leave in the 29-year-old left-hander to face Francisco Mejia.

Mejia promptly lined a double off the right-field wall, putting runners on second and third with no outs and ending Bumgarner’s night. Bochy summoned Reyes Moronta, who induced a run-scoring groundout from Manuel Margot that brought the Padres within one. Moronta’s next pitch yielded the biggest blow, as he surrendered a two-run, pinch-hit home run to Franmil Reyes that put San Diego ahead.

“He elevated a breaking ball,” Bochy said. “He’s not quite as sharp as we usually see him.”

It was a stinging defeat for the Giants, who have largely relied on their pitchers to keep them in games as their bats have struggled to consistently score runs this year. It wasn’t the only loss they endured, as outfielder Gerardo Parra also exited in the seventh inning after suffering a cut lip when a 93 mph fastball from Padres reliever Brad Wieck hit his shoulder and deflected to his face.

Bumgarner was charged with five runs on four hits over six-plus innings, falling to 0-3 to start the season for the first time since 2017.

“What makes it more difficult is to feel as good as I did and the command to be as sharp as it was and all that, and then to get the result that I did,” Bumgarner said. “That’s what makes it hard to swallow.”

Eric Lauer shut out the Giants on Opening Day in San Diego, exposing the club’s vulnerability against left-handed pitching at the outset of the season. But when Lauer faced the Giants for a second time, their lineup looked a little different.

In the 12 days since their season-opening loss, the Giants acquired a pair of experienced right-handed bats in Pillar and Tyler Austin. The newcomers made their impact felt, as Austin’s first hit with the Giants jumpstarted a five-run fourth inning that was capped by Pillar’s first career grand slam.

Austin, who was acquired from the Twins in exchange for Minor League outfielder Malique Ziegler on Monday, led off the fourth with a single, advanced to second on a walk from Brandon Belt and scored on Brandon Crawford’s RBI single down the left-field line to put the Giants on the board. Lauer then intentionally walked Yangervis Solarte to bring up Pillar with two outs and the bases loaded.

The gamble backfired. Pillar, who had been mired in a 3-for-33 (.091) slump to start the season, crushed a 2-0 fastball from Lauer out to left field for a grand slam, staking the Giants a 5-0 lead and matching the club’s run total over their four-game series in San Diego last month. It was the Giants’ first slam since April 8, 2017. They were the only team in the Majors not to hit one last season.

“You never like the guy to get walked in front of you,” Pillar said. “You kind of take that as a little bit of a sign of disrespect, but it’s part of the game. They tried to get him to chase. [Solarte] did a good job laying off pitches and when they fell behind [3-0], they tried to take their chance with the new guy.”

Bumgarner opened his start with four no-hit innings, but the Padres began clawing their way back into the game after Tatis crushed a two-run home run in the fifth to trim the deficit to 5-2. Bumgarner also gave up a leadoff homer to Wil Myers in the sixth, setting the stage for San Diego’s decisive rally in the following inning.

“I hate coming out on the losing side tonight,” Bumgarner said. “I feel like we played a good game. There was a lot of home runs. Too many home runs.”

Milestone strikeout for Bumgarner
Bumgarner picked up his 1,607th career strikeout after whiffing Luis Urias to end the third inning, overtaking Hall of Famer Gaylord Perry for seventh place on the Giants’ all-time strikeouts list. He ranks fourth among San Francisco-era pitchers, behind only Juan Marichal, Tim Lincecum and Matt Cain.