Spieth on a record Masters run to lead by five

Jordan Spieth of the U.S. hits off the fourth tee during second round play of the Masters golf tournament at the Augusta National Golf Course in Augusta, Georgia April 10, 2015. REUTERS/Brian Snyder

AUGUSTA, Georgia (Reuters) - Jordan Spieth threatened to turn the year's first major into a runaway as he fired a six-under-par 66 for a five-shot lead and a Masters record for lowest 36-hole total at Augusta National on Friday.

Playing with a steely focus and pinpoint precision, the 21-year-old Spieth reached the halfway mark on 14-under-par 130 to surpass the 131 posted by Raymond Floyd on his way to winning the 1976 Masters.