SAN FRANCISCO -- There was never much of a doubt that Logan Webb would be the Giants’ Opening Day starter. The bigger question at the outset of the spring was who would catch him and fill the cavernous hole that was left behind the plate following the retirement of franchise icon Buster Posey.

One day before the Giants kicked off their 2022 campaign, manager Gabe Kapler announced that the assignment would go to rookie Joey Bart.

“He’s ready for this,” Kapler said.

Friday afternoon marked a fresh start for not only the Giants, but also Bart, who officially ushered in the post-Posey era by crushing his first career Major League home run in a 6-5 walk-off win over the Marlins in 10 innings on Opening Day at Oracle Park.

“It was good to finally get it,” Bart said. “I feel like it’s been a long time coming. It was good to knock it out of the way and get the ball rolling.”

Brandon Belt and Thairo Estrada also homered as the Giants overcame a blown save from closer Camilo Doval, who gave up three runs in the ninth inning, including a two-run shot by Jazz Chisholm Jr. that briefly put the Marlins ahead, 5-4. A throwing error by Estrada helped fuel the Marlins’ late rally, but the 26-year-old second baseman redeemed himself by launching a game-tying homer in the bottom of the ninth to force extra innings.

Austin Slater followed with a walk-off double to left field that scored Darin Ruf from first base in the bottom of the 10th, giving the Giants their first win of the year. It was Slater’s first career walk-off hit and the Giants’ first walk-off win on Opening Day since April 6, 1987, against the Padres.

Webb was charged with one run on five hits over six-plus innings, picking up where he left off from his breakout campaign last year. Webb managed to pitch through a few mistakes from the Giants’ defense and overcame an injury scare in the third, when he suffered a mild right ankle sprain while attempting to field an infield single from Chisholm.

“A lot of it was Joey getting a feel for the game,” Webb said. “He was amazing back there today. It was really cool to see him hit a home run, too. It was overall just amazing to get back there and kind of get back to what we were doing.”

The homegrown battery of Webb and Bart could become an Opening Day fixture in San Francisco for years to come, particularly given the growth the 25-year-olds have shown in recent years. Webb developed into a bonafide ace by the end of last season, and Bart proved that he was ready to take the reins by showing that wasn’t the same guy who scuffled in his first taste of the big leagues two years ago.

There was, after all, nothing normal about Bart’s big league debut in 2020. He arrived in the middle of a global pandemic, with no fans in the stands and no Posey around to ease his transition to the Majors. The Giants didn’t have much of a choice but to rush his timeline after Posey elected not to play, and Bart predictably struggled, hitting .233 with 41 strikeouts over 103 at-bats.

“To get thrown into the spot he did two years ago, it’s like, ‘Well, what did you expect?’” veteran Curt Casali said. “It was out of necessity, and it was not his fault. He didn’t even do that bad, I don’t think. But he got a few games under his belt last year for us and helped us win a couple of games, which was enormous. And now in spring, he was kind of what we were all expecting Joey to be: To be the dude. His bat has looked really good. He’s been tremendous behind the plate as well. I expect huge things from him.”

Bart scored the Giants’ first run of the season in the third, drawing a walk and then scoring from first when Joey Wendle committed a throwing error on a bunt single from Belt. He later flashed his power by hammering a hanging slider from Miami right-hander Sandy Alcantara halfway up the left-field bleachers to extend San Francisco’s lead to 3-0 in the fifth inning.

Bart became the first Giant to collect his first career home run on Opening Day since Will Clark in 1986. After returning to the dugout, Bart was greeted with good-natured ribbing from his teammates, who had given him a hard time about taking so long to notch his first home run.

“He looked like a real big leaguer out there today,” Belt said. “It only took him two years to get a homer.”

“They’ve been chirping me for a while,” Bart said, grinning. “As they should.”

The Giants are hoping it’s just the first of many milestones for Bart, who has the potential to develop into a foundational piece for the franchise.

“It’s what you live for,” Bart said. “Personally, I’ve always been a guy that lives for that. I wouldn’t be here if I didn’t have that in my heart. I’m super excited about getting out here and coming out and competing and setting the tone.”