Golf's tumultuous start to the year became yet more contentious still on Sunday night when Dustin Johnson's victory over Rory McIlroy in the World Golf Championship in Mexico City was marred by a rules *controversy. Johnson, the former world No 1, shot a 66 to finish on 21 under to beat McIlroy by five strokes, with five more back to a group in third including England's Ian Poulter and Paul Casey. On the fifth hole at Chapultepec Golf Club, Johnson skewed his drive, with his ball coming to rest near a buggy path.