If this series is a playoff preview, the Cardinals are seeing a Padres team that might actually be ready. The Padres scored twice in the first inning, added a run in the fourth, another in the fifth and again in the seventh to beat the National League Central leaders 5-0 on Tuesday night at Petco Park. “We may see them again … in games that matter more in the next month,” Padres reliever Nick Martinez said. “We’re showing everyone who we really are when we bring the energy.” Mike Clevinger allowed three hits and no runs in 5 2/3 innings. It was his best outing in at least a month and extended …