SAN FRANCISCO -- The Giants lost their starting catcher and their leadoff hitter on Friday when Buster Posey landed on the injured list with a left thumb contusion and LaMonte Wade Jr. was scratched from the lineup with a left hand strain. But, as has become a recurring theme for the club this season, their substitutes stepped up to help fill the void.

Backup catcher Curt Casali and Darin Ruf, who replaced Wade at first base, each homered to power the Giants to a 5-3 series-opening win over the Nationals on Friday night at Oracle Park.

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“It’s just a total team effort,” Ruf said. “I think it starts with our pitching and our defense. It takes a lot of pressure off us offensively to not try to do more than you’re capable of. It’s about having quality at-bats. Luckily, the quality at-bats that a lot of us are having end in positive results.”

Ruf opened the scoring with a two-out RBI single in the first inning and then snapped a 3-3 tie by hammering a go-ahead shot off Nationals left-hander Sam Clay in the fifth. Wilmer Flores also went deep in the seventh to add an insurance run for the Giants, who improved to 55-32 entering the final weekend before the All-Star break.

The Giants now lead the Majors with 130 home runs this season, but their defense -- led by All-Star shortstop Brandon Crawford -- also put on a show to squash multiple threats from the Nationals.

“I think tonight is probably the first time I can say confidently that defense won the game for us,” manager Gabe Kapler said. “I think we’ve had moments where defense has helped us win games, but I really think it was the biggest difference-maker for us.”

With San Francisco clinging to a 4-3 lead in the sixth, Crawford made a diving stop on Tres Barrera’s sharp grounder up the middle and then executed a perfect glove flip to second baseman Donovan Solano to initiate a 6-4-3 double play.

In the seventh, Gerardo Parra drew a leadoff walk and advanced to third with one out, but the Giants nabbed him at the plate for the second time after Crawford ranged to his left to snare Trea Turner’s hard-hit grounder before firing to Casali to record the out at home. Crawford capped his defensive clinic by turning another key double play in the eighth, when he took a feed from Solano and rifled a throw to Ruf to get Parra at first base and help Tyler Rogers escape a bases-loaded jam.

“I just told him I thought that was probably one of the best defensive games I’ve ever seen,” Casali said.

Casali, who has started three of the Giants’ last four games since Posey went down with a left thumb contusion, finished 3-for-4 with two RBIs and finished a triple shy of the cycle. The 32-year-old veteran has enjoyed a significant offensive turnaround since returning from the injured list on June 12, going 16-for-40 (.400) with three home runs to raise his batting average from .100 to .215.

Posey’s resurgence has been an integral part of the Giants’ success this year, but it’s impossible to discount the contributions from Casali, who’s guided the club to a 23-6 mark in games he’s started this season.

“It’s never good when Buster’s hurt and he can’t be out there, and I’ll keep saying that,” Casali said. “But at the end of the day, I signed here to be able to contribute when he’s not in there. Hopefully it’s not a long stint on the injured list. It stinks that he’s probably going to miss the All-Star Game, but hopefully we’ll get him back really, really soon.”

Logan Webb fired three scoreless innings on 45 pitches in his first start since returning from the injured list, kicking off a bullpen game for the Giants. The Nationals scored three runs off left-hander José Álvarez to tie the game in the fourth, but John Brebbia, Jarlín García, Zack Littell, Dominic Leone, Rogers and Jake McGee put up zeros the rest of the way to shut the door for the Giants.

Webb, 24, missed 33 games with a right shoulder strain and made only one rehab start with Triple-A Sacramento before rejoining the rotation, but the Giants felt he was the best option to fill in for left-hander Sammy Long, who landed on the IL with a lower back strain earlier this week.

“I’ve kind of been itching to get back for a while now,” Webb said. “When they called me and they were like, ‘Hey, how do you feel about throwing on Friday?’ I was like, ‘Heck yeah!’ I’ve been waiting for this for a while.”

Despite not having a prolonged ramp-up to Friday’s start, Webb looked sharp before exhausting his pitch count. He allowed only one hit, a leadoff single to Starlin Castro in the second, and opened his outing by striking out the side in the first. Kapler described Webb’s sinker as “excellent,” highlighting the darting pitch he threw to strike out Juan Soto swinging in his first at-bat of the night.

“Looking back at the video of it, it’s probably the best sinker I’ve ever thrown,” Webb said. “Obviously, if I get a swing like that, it’s pretty encouraging for me. It shows where my stuff can be and what it’s supposed to be.”

“Trea Turner was like, ‘Why’d you guys take that guy out?’” Casali said. “It was really nice to see. I think we’ve been waiting a while to get Webby back. I thought he did great. He stayed within himself and put us in a great position to win the game.”