SAN FRANCISCO -- After securing a hard-fought series victory at Milwaukee over the weekend, the Giants found themselves tapping into their resiliency yet again in Tuesday night’s series opener against the lowly D-backs.

The Giants blew a five-run lead in the sixth inning and a two-run lead in the ninth, but they managed to rally for an 8-7 walk-off win on a two-out fielding error by D-backs first baseman Christian Walker.

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The D-backs scored two runs in the ninth off Jake McGee to tie the game at 7, but the Giants responded by staging the decisive rally in the bottom of the ninth against Matt Peacock. LaMonte Wade Jr. led off the inning by shooting a hard-hit liner to the right side that Walker misplayed, allowing Wade to reach on what was ruled a single. Buster Posey then walked to put a pair of runners on base with two outs for Kris Bryant.

Bryant followed with another blistered grounder to the right side that Walker couldn’t handle, allowing Wade to score the winning run from third and give the Giants their 13th victory in 15 games against the D-backs this season.

“I think the way our offense can put pressure on other teams, we feel like if we can keep it close, we feel like we’ve got a shot at any point in the game,” said Posey, who went 2-for-2 with a home run and three walks. “We’ve been able to do that. It seems like the last couple of weeks, we’ve had some back-and-forth games.”

The Giants have outscored the cellar-dwelling D-backs 107-63 during their season series this year, but they had to dig deep to pull out Tuesday’s win, which marked third-base coach Ron Wotus’ 2,000th victory with the club.

San Francisco scored four runs in the first inning against Arizona right-hander Zac Gallen and then extended its lead to 5-0 on Posey’s 14th home run of the year, a solo shot to straightaway center field in the fifth, but things quickly went sideways in the sixth.

Left-hander Alex Wood yielded only one hit over his first five innings, but he unraveled in his final inning, allowing the D-backs to rally for five runs to tie the game. Three consecutive doubles from Gallen, Nick Ahmed and Ketel Marte cut the Giants’ lead to 5-2, and Carson Kelly followed with a two-out RBI triple that eluded a diving Wade in right-center field. Asdrúbal Cabrera then drove a misplaced slider over the center-field wall for a game-tying, two-run home run.

Wood departed after giving up five runs on six hits over six innings, causing his ERA to climb to 4.22 on the season.

“He was really effective until that inning,” manager Gabe Kapler said. “I will also say he was very efficient, so he had plenty of pitches to work with. He was in his delivery, the ball was coming out good, the stuff was good. They just started banging him around the ballpark a little bit, and it happened really quickly.”

Still, the Giants regained the lead in the eighth on Brandon Crawford’s go-ahead double off lefty Joe Mantiply, which scored Posey all the way from first. After sliding safely across home plate, Posey got up and appeared to say, “I’m so fast,” to Bryant, which was partly backed up by the metrics. Posey’s sprint speed on the play was 25.2 feet per second -- below the league average of 27 feet per second, but well above his season average of 24.3 feet per second, according to Statcast.

“It was most definitely sarcasm about being fast,” the 34-year-old Posey said. “I was just happy that I made it there. When I saw Wo waving me, I knew it was probably going to be close.”

The Giants added another run on Sean Poppen’s errant pickoff throw to first base, which allowed Crawford to score from third and give the team some additional breathing room that proved critical the following inning.

McGee took over in the ninth, but he fell into trouble after giving up back-to-back singles and a walk to load the bases with no outs. He struck out Josh Rojas looking for the first out, but pinch-hitter Josh VanMeter then worked a walk to force in a run and bring the D-backs within one. Ahmed followed with a game-tying sacrifice fly, prompting Kapler to bring in Zack Littell to replace McGee, who was charged with his first earned runs since May 30.

In the end, though, the Giants found a way to win, improving to a Major League-best 72-41 to stay four games ahead of the Dodgers in the National League West.