Masters champion Adam Scott, U.S. Open winner Justin Rose and Jason Dufner, victorious earlier this month at the PGA Championship, will each be making their first appearances in the exclusive event that annually brings together the winners of golf's biggest titles.
British Open champion Phil Mickelson declined his invitation, reportedly due to an 'end-of-season scheduling conflict.' It's the third time Mickelson has opted to skip the event, having failed to return to the field since he made consecutive appearances in 2004 and 2005 when the event was held in Hawaii.
As defending champion of the event, Harrington was the first alternate in line and will take Mickelson's spot. It marks the fourth Grand Slam appearance for the Irishman, who also was runner-up in both 2007 and 2008.
The PGA Grand Slam of Golf will be held Oct. 14-16 at Port Royal Golf Course.