By Tony Jimenez TROON, Scotland (Reuters) - The so-called 'Big Four' of world golf were left trailing in the wake of the leaders for the second day running at the British Open on Friday. World number two Dustin Johnson (69) and fourth-ranked Rory McIlroy (71) were the best-placed of the quartet on two-under-par, eight adrift of championship pacesetter Phil Mickelson. Top-ranked Jason Day (70) was 11 shots behind American Mickelson while number three Jordan Spieth (75) just made the cut on four-over. More...