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.
"It's cool. Any time you can set a record here is pretty awesome," said Spieth. "I'm very excited about today and the way I struck the ball."
Spieth, with 15 birdies and one bogey in his two rounds, also equalled the lowest 36-hole total for any major championship.
Spieth led by five over compatriot Charley Hoffman, who registered five birdies but bogeyed the last for a 68 and nine-under 135 on a hot, humid day amid the Georgia pines.
Dustin Johnson set another Masters mark as he flew up the leaderboard with a record three eagles on the par-fives to record a 67 for seven-under 137.
Former U.S. Open winner Justin Rose (70) and fellow Englishman Paul Casey (68) were also on 137.
One shot farther back was three-times winner Phil Mickelson, who made four birdies on the back nine for a four-under 68 and a 138 total.
Tiger Woods climbed up the leaderboard as the four-time champion shot a 69 to stand two-under and tied for 19th. He had shared 41st place after an opening 73 in his return to competition following a two-month absence.
"I was at a pretty low one in my career, but to basically change an entire pattern like that and put it together and ... compete in a major championship like this is something I'm very proud of," he said.
World number one Rory McIlroy, who needs a Masters victory to complete a career grand slam, looked as though he might miss the cut when he went out in four-over 40 to stand three-over.
But the 25-year-old Northern Irishman posted 31 on the back nine for 71 to join Woods on 142.
Two-time champion Ben Crenshaw shot 85 for 32-over 176 in what was his last round at the Masters. He was given an emotional send-off at the 18th by fans, family and friends.
The cut was set at two-over-par 146 with 55 advancing to weekend play.
U.S. Open champion Martin Kaymer (151), former world number one Luke Donald (147), three-times major winner Padraig Harrington of Ireland (149) and twice Masters winner Tom Watson, who shot 81 on Friday, all missed the cut.
Spieth, not among the game's longest hitters, served notice last year that his game was fit for competing at Augusta National as he finished tied for second.
"What I learned was patience," he said about his 2014 showing. "I'm not going to get ahead of myself, I'm going to stay in the moment."
The young American began the day with a three-shot lead after a sizzling first-round 64.
On Friday, he made three birdies in a bogey-free front nine and matched that on the homeward half as he equalled the widest 36-hole lead at the Masters.
Other possible Masters milestones loom for Spieth, should he maintain his Augusta assault.
Woods won his first Masters in 1997 with a record low total of 18-under 270 for a record 12-shot victory margin -- both could be achievable for the 21-year-old.
One of Woods's Masters records was safe from Spieth, who would be the second youngest player to wear the green jacket should the Texan go on to win his first major.
"As far as history and what happened the last couple days, doesn't mean anything unless I can close it out," said Spieth.
"I don't want to go in as the 36-hole best record, but somebody who didn't win."
(Editing by Andrew Both/Gene Cherry)