"It was a long day and I began to get a little distracted, so, yes, that was a reason for that (bogey), " said Rose, who collected four pars before play was halted on the 17th.
After McGrane had holed for a bogey, Hamill was left with a ten-footer to prolong the play-off but the putt slid by leaving Harrington with the 20, 000 Euro first prize.
Earlier, Scotland's Marc Warren had held a two-stroke lead with three holes to play, but a three-putt contributed to a double bogey at the 16th which he followed with a bogey at the 17th.