SAN FRANCISCO — From the moment pitchers and catchers arrived at spring training, everything about the Giants and Dodgers was supposed to be a mismatch.

The Dodgers had the better rotation, the more experienced bullpen, the deeper lineup, the most recent World Series title and the far more realistic opportunity to win the next.

The National League West isn’t decided over Labor Day weekend, but with all 19 head-to-head matchups between the Giants and Dodgers in the books, there’s no longer any reason to doubt San Francisco. With a 6-4 victory at Oracle Park on Sunday, the Giants won the season series over the Dodgers 10-9 and now hold a one game lead in the division with 25 left to play.

The Giants held a 6-2 lead entering the ninth inning, but after Austin Barnes reached on a throwing error from third baseman Kris Bryant, Albert Pujols launched a two-run home run into the left center field bleachers to put the Dodgers within striking distance. San Francisco closer Jake McGee allowed a one-out single to Max Muncy, but retired Mookie Betts and Justin Turner to end the game.

A win in Sunday’s matchup, when the Giants appeared to be at an overwhelming pitching disadvantage, only validated the club’s belief it can race to the finish line and fend off the Dodgers. Los Angeles had ace Walker Buehler on the mound against a Giants team that had nine members of its bullpen combine to cover nine innings.

“Looking at things on paper, you know you have your work cut out for you,” Kapler said. “You have arguably one of the top three pitchers in the National League in Walker Buehler, their full lineup is out there and in a bullpen game, they’ve got lefties and righties who can really mash.”

Buehler entered Sunday’s start as a front-runner for the National League Cy Young Award and his dominance against the Giants has played a significant role in shaping his candidacy. In five starts against San Francisco, Buehler had logged 34 innings and only allowed three earned runs.

By the time the bottom of the fourth inning started on Sunday, Buehler was out of the game.

The Giants became the first team to score six runs against the Dodgers star this year as Brandon Belt launched a first-inning home run, Steven Duggar yanked a two-run triple down the right field line in the second and LaMonte Wade Jr. and Brandon Crawford drilled back-to-back doubles in the third, which all played a role in forcing Dave Roberts to go to his bullpen ahead of schedule.

Belt became the second Giants player to homer off Buehler this year with a 420-foot shot over the right center field wall that likely would have been a triple in the first two decades of Oracle Park’s existence. Thanks to the changes made to the ballpark prior to 2020, the solo home run gave the Giants a lead they wouldn’t relinquish.

Duggar hasn’t been on the roster since August 7, but the Giants promoted him from Triple-A Sunday after outfielder Austin Slater was placed on the seven-day concussion injured list following a crash into the center field wall in the first inning on Saturday.

“I was mentally preparing to come back since the second I got optioned,” Duggar said. “Really just tried to turn the page, keep it moving and to get a text this morning from skip that we’re in there, I was just ready to roll.

After homering off Buehler in an 8-5 Giants win on May 28, Duggar returned and made his presence felt with a triple from the No. 8 spot in the order.

“I thought he set the tone with the swing and I also thought he set the tone with the baserunning,” Kapler said. “Triples are pretty exciting. We don’t hit many of them. I don’t think it’s any secret we’re not the fastest team in the land, but Duggar can really run. I think that was a fire up the dugout moment.”

The extra-base hit forced Kapler to remove Zack Littell, who escaped a second-inning jam created by lefty José Álvarez, but the move paid off when pinch-hitter Darin Ruf looped a two-strike RBI single into center field to bring home Duggar.

Following third-inning RBIs from Crawford and catcher Curt Casali, the Giants held a five-run lead thanks to their biggest offensive outburst since the club scored eight runs on August 24 against the Mets.

Kapler had used up almost half of his available arms when the Dodgers brought in their first reliever, but that was by design for a Giants club that lost lefty Alex Wood to the COVID-19 injured list and righty Johnny Cueto to the 10-day injured list with a right elbow strain.

“We don’t panic,” Belt said. “We’ve been in some tough situations before, but there’s no panic. We really, genuinely feel like we have a chance to win the ballgame no matter what the score is and I think that’s helped us throughout the year.”

A day after opener Jay Jackson was charged with three earned runs in the first inning against the Dodgers, the Giants used one of their set-up men, Dominic Leone, to record the first three outs of Sunday’s game.

Leone, Álvarez, Littell, Jackson and lefty José Quintana covered the first 4 2/3 innings for the Giants before Kapler inserted rookie Camilo Doval into a high-pressure, bases loaded situation in the fifth. The right-handed flame-thrower fired the first pitch he saw to the backstop and issued a walk to Will Smith after a borderline 3-2 call went in favor of the Dodgers, but rebounded by striking out Chris Taylor to keep a four-run lead intact.

“Camilo did a really nice job of collecting himself,” Kapler said. “I thought he did a really nice job of getting back in the strike zone. Then he was able to give us parts of two innings, which I don’t know we were anticipating early in the game.”

No one anticipated much before the season and few anticipated Sunday unfolding as it did.

That’s the story of the Giants’ season.