Zack Greinke's poor opening day start came as a shock to many. After not giving up six runs in a single game all last season, the 32-year-old Arizona Diamondbacks pitcher gave up six runs in a single inning Monday. Greinke, who threw at least six innings in every start last year , was pulled after just four in his debut with the D-Backs. He allowed a total of seven runs. [Related: Zack Greinke was deemed one of the losers of opening day by The Stew ] For all of those reasons, it was an uncharacteristic start for the usually dominant Greinke. While some will want to blame expectations or opening day jitters, it appears another factor may have played a big role in Greinke's struggles. Sources: #Dbacks ' Greinke pitched with flu. Did not come close to missing start; decision that he would pitch was made day before. — Ken Rosenthal (@Ken_Rosenthal) April 5, 2016 According to Ken Rosenthal of Fox Sports, Greinke was feeling under the weather before his start. Though, as Rosenthal notes, the club never seriously considered moving Greinke out of his spot. He was deemed healthy enough to pitch on opening day the night prior to his start. If true, that probably explains his poor stat...