SAN FRANCISCO -- Giants pitching prospect Logan Webb certainly looked at home in his Oracle Park debut.

The 22-year-old right-hander allowed only one run over 5 2/3 innings in his third Major League start, but the Giants squandered his effort after Manny Machado tripled and scored the go-ahead run in the eighth inning to help lift the Padres to a 4-1 win on Saturday night.

San Diego added a pair of insurance runs in the ninth on Wil Myers’ two-run home run off closer Will Smith to take a 2-1 series lead ahead of Sunday’s finale.

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With the Giants’ (66-69) playoff hopes looking increasingly dim, the focus has now begun to shift more toward the future. They will use the final month of the season to evaluate young arms like Webb, who has the potential to play a bigger role in the 2020 rotation if he shows he can consistently replicate the performance he delivered Saturday.

Webb scattered seven hits while walking one and striking out seven, showing impressive poise and resilience on the mound. The Padres put a runner on base in five of Webb’s six innings, but he deftly navigated through traffic and opened his outing with five scoreless innings.

“He did a nice job,” manager Bruce Bochy said. “I like his makeup. He’s got confidence, poise. He’s got good stuff to work with. Good secondary pitches along with the good fastball. He commands it well. He’s aggressive out there, and he’s not going to back off. He’s got a great way about him.”

Webb began the sixth by striking out Machado on a nasty slider and coaxing a groundout from Eric Hosmer, but he lost his shutout bid after Josh Naylor doubled and scored on Manuel Margot’s RBI single to tie the game at 1.

“I was pretty disappointed I couldn’t get out of it,” Webb said. “I wish I could have gotten out of it a little earlier and possibly gone out for another one to give our bullpen another inning. Unfortunately, I couldn’t.”

Webb exited after throwing 91 pitches and was replaced by Reyes Moronta, who was soon forced to depart his relief outing after suffering an acute right shoulder strain.

Moronta dropped to the ground after throwing a 2-0 fastball to Luis Urias, grimacing in pain and receiving immediate medical attention from team athletic trainer Anthony Reyes and Bochy. Moronta spent a few minutes on the ground before walking off the field alongside Reyes. He will undergo an MRI on Sunday.

Tyler Rogers subsequently entered the game and walked Urias before inducing a groundout from Austin Hedges to preserve the tie. Still, the Padres came back to rally in the eighth after Machado tripled off Tony Watson and scored the go-ahead run on Naylor’s single to left field.

Austin Slater homered off Padres left-hander Joey Lucchesi to put the Giants on the board in the first inning, but they were held scoreless for the rest of the night. Their best scoring opportunity came in the sixth, when they loaded the bases with one out, but Lucchesi coaxed an inning-ending double play from newcomer Mauricio Dubon to shut down the threat.

Webb made his first two starts for the Giants on the road and said he experienced some jitters before taking the mound at Oracle Park for the first time.

“But it was good nerves,” Webb said. “It wasn’t bad nerves. It was excited nerves.”

He was tested early after the Padres put runners on the corners with one out in the first inning, but he came back to strike out Eric Hosmer on a slider and Naylor on a fastball to extricate himself from the jam.

While he fell one out shy of recording his first quality start for the Giants, Webb received a standing ovation from the fans at Oracle Park after completing his outing, which helped assuage some of his disappointment.

“I think growing up as a kid, that’s what you want,” Webb said. “One day, you hope to see that. It was pretty cool just looking up and seeing everybody. It was awesome.”