(adds latest scores) By Tony Jimenez TROON, Scotland, July 16 (Reuters) - Phil Mickelson and Henrik Stenson were threatening to turn the 145th British Open into a two-man slugfest after 12 holes of the third round on Saturday. It was a case of parry and thrust from the American and the Swede as Royal Troon showed its teeth for the second day running, with the winds whipping up to 25mph on the west coast of Scotland and making good scoring extremely tough. Mickelson, 46, who has led the championship since day one, made an early birdie at the third but that was matched by his Swedish playing partner who had also picked up a shot at the first. More...