SAN FRANCISCO — The swing was so pure that it left a mark. On Tony Vitello. From Drew Gilbert. “It was such a pretty swing, Drew punched me,” the Giants manager said after his club rallied against the Marlins for a 6-3 win Sunday. “And [he] said, ‘That’s the swing!’” The Giants’ Casey Schmitt delivered big hits on consecutive days against the Marlins in San Francisco. Getty Images While Casey Schmitt’s go-ahead home run in the seventh was a quality hack in its own right, the cut that caused a stir in the dugout came an inning earlier and got the comeback started. The Giants hope it can be the start of something much bigger. Almost a month in, Rafael Devers’ season-long slump has officially become a concern. Two soft outs on uncompetitive cuts in his first two at-bats Sunday did nothing to alleviate those worries. But after Schmitt drew a walk to lead off the sixth, Devers changed course.…