Ausmus is one of the best defensive catchers in the majors, winning Gold Gloves in 2001 and 2002. But he had a rare mental lapse in the ninth that caused lots of confusion and led to a loss for the Astros.
Miguel Cabrera followed with a chopper down the third-base line.
Jose Vizcaino jumped to catch the high hop and landed with his right foot on third base before throwing home.
Ausmus was unaware that Vizcaino had touched the bag, removing the force, and failed to tag Pierre before throwing to first. Home plate umpire Kerwin Danley initially ruled Pierre was out at home before being corrected by Jim Joyce, who made the call at third base.