American Bubba Watson charged into a three-shot lead at the halfway stage of the Masters with a second round 68.
The 2012 champion finished on seven under par, three shots ahead of Australian John Senden, with Dane Thomas Bjorn, Sweden's Jonas Blixt, defending champion Adam Scott and American Jordan Spieth on three under.
After shooting a bogey-free opening 69, Watson took his flawless stretch to 26 holes before a bogey at the ninth, where his approach bounced through the green and he failed to get up and down.
He made amends on the back nine with a sizzling streak that started with a superb tee shot at the difficult short 12th that gave him a two foot putt for birdie. He caught a break at the par-five 13th when his tee shot clipped the top of a tree along the right side and dropped safely on the edge of the fairway, but he took advantage by firing his approach to 12 feet and two-putting for another birdie.
At 14 he sank a 35-foot, right-to-left curling downhill putt that produced a huge roar from the galleries.
He chipped to four feet and sank the birdie putt at the par-five 15th, and holed a five-foot birdie at the par-three 16th to cap his dazzling run.
Watson withdrew from his last event after blaming an opening 83 at the Arnold Palmer Invitational on his head being "all discombobulated" due to severe allergies.
But the 35-year-old from Bagdad, Florida, did claim his first PGA Tour title since the Masters in February, shooting back-to-back bogey-free rounds of 64 to win the Northern Trust Open.
Senden moved to within three shots of the lead after a composed 68.
He was two over par through four holes of his second round, but six birdies in his next 11 saw him rocket up the leaderboard.
Bjorn had been 51 over par for his previous 10 Masters appearances before rounds of 73 and 68 this week, the 43-year-old Dane recording four bogeys and eight birdies, four of them coming in the last five holes.
Augusta specialist and 1992 champion Fred Couples is a further shot back on two under, the 54-year-old looking to become the oldest ever major winner after a 71.
Scotland's Stephen Gallacher was also delighted with his second round, a 72 leaving him one under and safely inside the halfway cut on his Masters debut.
Former Open champion Louis Oosthuizen, who lost a play-off to Watson in 2012, held a share of the lead when he holed from five feet for an eagle on the 13th.
But the South African then ran up a triple-bogey eight on the 15th after chipping from the back of the green into the water at the front, before a bogey on the 18th meant a round of 75 and left him level par for the tournament.
Lee Weswood is also level par after a one under 71 on Friday, while his fellow Englishmen Ian Poulter and Justin Rose both shot two under 70s to get back to two over for the tournament. Pre-tournament favourite Rory McIlroy shot a 71 on Thursday but slumped to a second round 77, making a four-foot putt on the last to survive right on the cut-line on four over.
But three-time Masters champion Phil Mickelson suffered a first missed cut since 1997.
He suffered a triple-bogey on the short 12th, where he amazingly went from the front bunker to the back bunker and back into the front bunker again.
It was to Mickelson's credit that he played the final six holes in two under but the damage was done and he finished on five over par after signing for a 73.