The St. Louis Cardinals begin a crucial three-game set with the Athletics on Tuesday night as they continue their stretch against playoff contending teams. They are 23-17 and sit in third place in the crowded National League Central , 3 1/2 games back of the first place Chicago Cubs. If there is one area of weakness, it would be their starting rotation. With Sonny Gray gone, they no longer have a true ace. Their best starter has been Michael McGreevy, but he still isn't exactly ace material. Kerry Miller of Bleacher Report ranked all 30 major league teams' rotations and was pretty accurate with the Cardinals, putting them at No. 22 out of 30 "Cardinals pitching has been better than expected, but also luckier than deserved," Miller wrote. "They have the most concerning ratio of ERA (3.96) to expected ERA (5.11), which predominantly stems from the fact that they generate strikeouts at nearly the lowest rate in the majors.…