The struggles in the first inning Tuesday for rookie Michael Wacha were so uncharacteristic and the Mets’ responses to his changeup so unusual that teammates, including Adam Wainwright, left the dugout to dissect video of the inning for an explanation. They studied to see if Wacha was tipping pitches. They studied to see how Wacha’s delivery was disjointed. They studied. Wacha corrected. To begin his third major-league start, Wacha walked three batters and allowed two runs before he got a third out. But he recalibrated his fastball and fixed his hasty mechanics on the fly to complete six innings and follow the offense to a 9-2 victory at Citi Field. The win was his first in the majors – only 372 days after the Cardinals selected him 19th overall in the draft. “You throw 37 pitches in the first inning and you’re typically not going to be around very long,” manager Mike Matheny said. “We’ve said this quite a few times about these young pitchers: There’s a lot of excitement around them right now, and rightfully so. But I think you really find out about them when things don’t go exactly as scripted. Michael had one of those nights. He got better as he went.” By surviving the first inning and thriving by the third, Wacha (1-0) stayed in long enough to still be pitching when the offense stirred. Mets starter Jeremy Hefner (1-6) could not get through the middle of the order a third time. Matt Holliday had his second of three hits and Allen Craig hit a three-run home run in the fifth inning as the Cardinals reversed the Mets’ 2-0 lead and sparked a rout. For the fourth consecutive game, all of the Cardinals’ position players reached base in the same game. David Freese extended his hitting streak to 20 games, the longest active streak in the majors. Wacha drove in the tying run for his first big-league RBI.