Just 18 games into the season, the Astros’ elevator to Class AAA Oklahoma City is already running strong. Pitchers Dallas Keuchel, Edgar Gonzalez, Brett Oberholtzer and Paul Clemens have been called up. Keuchel also has been sent back down, while Xavier Cedeno and Gonzalez have been designated for assignment. Reliever Travis Blackley was acquired in an early season trade. Rule 5 pick Josh Fields was placed on the disabled list. Throw the names together, add in Astros starting pitchers who often have struggled to reach six innings and a team that posts an MLB-worst 5.40 ERA, and the organization has quietly introduced tandem pitching units to the big leagues during [...]