Gusting winds created second-round havoc at Augusta National but could not blow Jordan Spieth from the top of the Masters leaderboard on Friday while helping lift Rory McIlroy's career grand slam bid.
When the dust had settled on a windy day that kept the Georgia pines bending and pin flags waving, defending champion Spieth was still holding top spot -- but just barely when a five-shot lead was chopped to a single stroke after an adventurous two-over 74.
McIlroy, who began the day four shots behind the pacesetting Texan and fell a massive eight back with seven to play, stormed into contention with a blistering back nine charge and the help of a late Spieth stumble.
Northern Irishman McIlroy appeared headed in the wrong direction as he covered the outward nine in one-over but caught fire after the turn, plundering three birdies over his final six holes for a 71, matching the lowest round of the day.
Should the world number three triumph on Sunday, he would become only the sixth man to win all four of golf's blue riband events, joining Tiger Woods, Jack Nicklaus, Gary Player, Ben Hogan and Gene Sarazen.
"Look, I'm really trying to block that out," four-times major champion McIlroy said. "I'm trying to beat guys on this leaderboard that I've beaten before, so I need to take confidence from that and know that I've been in this position before.
"Maybe not on this golf course, but I've been in this position before in big tournaments and been able to get the job done. So that's the way I need to approach it."
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New Zealand's Danny Lee (74) and American Scott Piercy (72) sit two off the lead with Japan's Hideki Matsuyama (72), Denmark's Soren Kjeldsen (74) and American Brandt Snedeker (72) one further back after a wild and woolly day that saw just seven men under par as the year's first major hit the midway mark.
Spieth had slept on a two-shot overnight cushion and by the time he stepped onto the first tee to start his second round his advantage had grown to three with none of the early starters able to mount a serious challenge.
The world number two went quickly to work, drawing a huge roar from the large gallery tracking him when he rolled in a 14-foot birdie putt at the first that put even more pressure on the chasing pack.
Spieth continued to pull away with an easy birdie at the third after a pinpoint approach left him with a two-foot putt to get to eight-under.
But danger lurks everywhere at Augusta National, and Spieth found it at the par-four fifth where he four-putted and ran up a double bogey that slashed his advantage to three.
Spieth hit back with a birdie at the eighth but stumbled through the turn with bogeys at nine and 10 followed by back-to-back bogeys at 16 and 17 before a draining a nervy 14-footer for par at the 18th to keep the outright lead.
It marked the sixth consecutive round Spieth had sat alone atop the Augusta leaderboard, something never done before at the Masters.
"It was tough. It was very tough," said Spieth. "We kept reminding ourselves that even par is a good score, even par is a good score.
"But boy, that golf course changed very much throughout the day. We were trying to adjust with the ever gusting and changing winds. That was a hard golf course."
World number one Jason Day's struggles continued as he grinded out a one-over 73 but the Australian ended the round just five strokes off the pace and still very much in contention.
The devilish winds did blow plenty of contenders off course, including one of the pre-Masters favorites in world number five Rickie Fowler, three-time champion Phil Mickelson and 2011 winner South African Charl Schwartzel.
Eight-times major champion Tom Watson also missed the cut and took a final bow at Augusta National, shedding a tear as he walked up to the 18th green in what was his 43rd and final Masters.