Clarke Paul BroadhurstThey were at 9 under overall after round three, but it was Harrington (a three-time major winner) who surged into contention at Gleneagles, posting a 3-under 67 to put pressure on Clarke on the final hole.
Clarke, 53, held firm with a birdie for a 69 to finish at 10-under 270 overall. He also added a senior major in his Claret Jug at 2011s British Open.
Play was stopped by heavy rains in the early evening. Clarke, Broadhurst and Broadhurst still had five holes when play resumed at 8:08 p.m.
Argentine Mauricio MolinaAmerican Doug BarronBoth posted 65s to finish in a tie for third place at eight under with four-time major champ Ernie Els (68), Thongchai Jaidee (68), Steven AlkerBroadhurst and (70).
Broadhurst finished one shot ahead Scotlands with a 1-over-71, and fell back. Colin MontgomerieAfter he reached a 69.