Since joining the Major League umpiring staff in 2000, O'Nora has worked the 2004 National League Division Series, the 2006 National League Division Series, the 2009 National League Division Series, the 2010 American League Division Series, and the 2012 National League Division Series. He also umpired the 2008 American League Championship Series and the 2012 World Series. He was a part of the crew that worked in the 2000, 2010, and 2019 Major League Baseball All-Star Games.