(Adds details, quotes) May 31 (Reuters) - American Bubba Watson surged to the lead as Englishman Paul Casey plunged four strokes behind after the third round of the Memorial tournament in Dublin, Ohio on Saturday. Masters champion Watson used his astonishing power to compile five early birdies on his way to a three-under-par 69 in ideal conditions at Muirfield Village. He posted a 12-under 204 total, one stroke ahead of compatriot Scott Langley (67) with one round left. Young Japanese player Hideki Matsuyama (69) was two strokes behind, while world number one Adam Scott of Australia (68) trailed by three despite a bogey at the final hole. Click here to read full news..