Neither rain, nor delay, nor pressure, nor glare of October lights keeps Michael Wacha from the usual swift completion of his assigned starts. The young righty has shown whatever the conditions, he can deliver. For the third time in as many starts this season, Wacha had an outing complicated by soggy weather and for the third time the second-year starter provided the Cardinals with at least six solid innings and a chance to win. The lineup backed him and twice rallied for him Sunday to complete a 6-4 victory against the Cubs in front of a sellout crowd of 44,135 at Busch Stadium. The win completes a 4-2 homestand and sends the Cardinals to Milwaukee, where the surging Brewers and their nine consecutive wins await. Closer Trevor Rosenthal allowed a run to score, and the tying run to reach base, in a listing ninth inning before claiming his fourth save. Matt Carpenter was involved in the Cardinals’ first four runs Sunday, and his sacrifice fly put the Cardinals ahead for good after a 46-minute rain delay in the third inning. “One of the five starters is always the rain guy,” pitching coach Derek Lilliquist said. “Just deal with it. He doesn’t think much more than one pitch at a time, which is golden.” If he wanted to, Wacha has had plenty of time to ruminate on every pitch this season, what with a 10-minute delay to his start at the home opener and the 2-hour, 40-minute delay that pushed back his season debut in Cincinnati. His first major-league start, in May of last season, included the longest delay of the year and forced the game to finish at 3 a.m. St. Louis time. He had two other games that extended to at least 14 innings after he left. Off to a 2-0 start with a 1.89 ERA, he has been the rainmaker. He’s also been Teflon with distractions. Though he’s made only 17 starts in his career, including the playoffs, he’s pitched in elimination games, in clinchers, in a near no-hitter and at Fenway Park in the World Series. Minor potholes such as an early homer or game-tying single weren’t going to slow him.