There is no alternate explanation for what this 25-year-old rookie accomplished Saturday in a 3-0 victory against the Dodgers and Clayton Kershaw that assured the Giants will play beyond Sunday. Blach was throwing at AT&T Park for the first time, in his fourth big-league game, being caught by Buster Posey for the first time, and none of that mattered in his first career win. […] Blach held the regular Dodgers lineup to three hits in eight innings and became the first Giant in 25 years to pitch that many shutout frames in a start within his first four big-league games. With Angel Pagan homering off Kershaw in the fifth to break a scoreless tie, then singling to start a two-run insurance rally in the seventh, the Giants maintained a one-game lead for the second wild card. After Matt Moore faces Kenta Maeda on Sunday, the Giants will end Game 162 no worse than tied for that final playoff spot. A Giants win or Cardinals loss will send the Giants to the postseason for a fourth consecutive even-numbered year. If the Giants lose and Cardinals win, the Giants fly to St. Louis for a Monday play-in for the right to face the Mets in the wild-card game in New York on Wednesday. Blach threw 99 pitches in the best start by a Giant this early in his career since Mike Remlinger shut out the Pirates in his 1991 debut. When Blach threw his final pitch past Kiké Hernandez’s bat for strike three, he bounced off the mound, pumped his fist and ran to the dugout as he does after every inning. The energy from the crowd soared with each shutout inning and peaked in the seventh, when Blach struck out Yasiel Puig. “I didn’t know he’d give us eight shutout innings, to be honest,” Bochy said. If the Giants win Sunday or the Cardinals lose, S.F. will claim the second wild-card spot and travel to play the Mets in Wednesday’s wild-card game. The winner claims the second wild card-spot and travels to play the Mets in Wednesday’s wild-card game.