On paper, the Padres built one of the best bullpens in baseball this offseason. But through six games, there’s only one thing standing between San Diego and a 6-0 start -- that very bullpen.

The Padres entered the eighth inning at Oracle Park in cruise control on Wednesday night. But they left themselves open to a pair of Giants sucker punches. Donovan Solano tied the game with a three-run shot off Craig Stammen in the eighth. An inning later, Mike Yastrzemski sealed a 7-6 Giants victory with a walk-off blast into McCovey Cove against lefty Matt Strahm.

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“This one hurts tonight,” said Padres manager Jayce Tingler. “... The bottom line, you’ve got to finish.”

The implosion canceled out a strong early showing from the San Diego offense. Manny Machado launched a two-run homer in the top of the third inning, and Trent Grisham followed with a three-run blast in the fourth. But for the second time in four days, the Padres lost a game in which they held a lead entering the eighth and were tied entering the ninth.

Ahead 6-3 in the eighth, Tingler called on Stammen, the veteran righty who had returned to San Diego on a one-year deal during the offseason. Stammen allowed two quick baserunners, giving the new Padres skipper one of his first tough decisions. He stuck with Stammen.

“Craig’s certainly trustworthy, it just didn’t happen tonight,” Tingler said. “Craig’s one of our leaders, he’s one of our better guys. You feel good when you give him the ball, especially with a lead. If I had the chance again, it’s going right back to him.”

Stammen’s fourth pitch to Solano was a tailing two-seamer at 89.4 mph, well below his average of 92.2 from last season. It was an inch or two inside, but Solano turned on it anyway, sending it into the left-field seats.

After Austin Slater’s ensuing single, Strahm was summoned to escape the eighth inning, and he did. But in the ninth, Strahm’s 2-2 fastball to Yastrzemski caught too much of the inside corner, and the Giants center fielder sent it soaring into the night.

“We felt we had the guys in there we wanted,” Tingler said afterward, but there may have been other factors at play in his late-game decision making.

Emilio Pagán and Drew Pomeranz were excellent at the back end on Tuesday night. But the Padres resolved not to use them on back-to-back days. It’s already clear that Tingler is doing his best to preserve his arms for the long haul. With 30 games in the season’s first 31 days, Tingler indicated that he’ll continue to use rest days for his relievers early in the season.

“We talked early today about giving them the day off tonight if we could,” Tingler said. “We had it drawn up. We felt good with Craig in the eighth, then trying to get the ball to [closer] Kirby [Yates]. It just didn’t work out tonight.”

Grisham stays hot

One of the Padres’ most unheralded moves of the offseason is paying the biggest dividends. San Diego landed Grisham from the Brewers in the trade that sent Luis Urías to Milwaukee. And suddenly the Padres might have found their center fielder of the future.

Grisham went 2-for-4 on Wednesday with a walk and a three-run homer that put the Padres on top 6-2 in the fourth inning. His other hit? A perfect bunt single to left of Giants first baseman Pablo Sandoval.

“Any time you get a bunt hit and a three-run bomb in there, that’s a pretty good mixture,” Tingler said.

Grisham is reaching base at a .417 clip, and he has now homered twice in three games.

Blunders on the bases

The Padres entered play first in the Majors with seven stolen bases. But there’s a price for that aggression on the basepaths, and they paid it in a big moment on Wednesday.

With a three-run lead in the top of the eighth, Padres left fielder Edward Olivares walked, then was picked off at first base by Giants lefty Tyler Anderson. The next batter, Fernando Tatis Jr., did the same.

“It’s a little bit of give and take, but we’ve got to recognize we haven’t been very good with the lefties on the mound and the pickoff,” Tingler said. “We can’t be giving outs away."

TV cameras caught Tatis mouthing the words, “Is that a balk?” to first-base coach Wayne Kirby after his pickoff. It certainly seemed close. But Tingler wasn’t ready to use that as an excuse.

“Lefties in the league, it’s pretty consistent that guys work that line, and it’s rarely called,” Tingler said. “The bottom line is: We as coaches have to do a better job to prepare our guys, and we can’t be giving outs away, especially in the eighth inning.”

And especially considering what came next.