Bubba Watson continued his impressive bid for a second Masters title in three years on Friday as Thomas Bjorn became Europe's leading contender for a first victory since 1999.
Watson was the only player in the 97-strong field to card a bogey-free round on a testing opening day at Augusta National, the left-hander's 69 containing three birdies and 15 pars.
And although the flamboyant world number 12 finally dropped a shot on the ninth hole of his second round, birdies on the seventh, 12th, 13th and 14th took the 2012 champion into the lead on six under par.
Kevin Stadler, KJ Choi and overnight leader Bill Haas were all four under, but with the wind strengthening Bjorn was delighted to be safely in the clubhouse on three under.
"I'm going to hit some balls for 20 minutes and then go home and put my feet up," Bjorn said after a 68 which featured four birdies in his last five holes.
"It was a good day. I played well all the way through and felt comfortable on the golf course today. I hit two great shots into 13 and walked off with a par and after that decided I needed to be more aggressive.
"I took the shots on at 14 and 16 and they paid off and it was nice to walk up and tap it in for a birdie on 18."
Scotland's Stephen Gallacher was also delighted with his second round, a 72 leaving him one under and guaranteed to make the halfway cut on his Masters debut - something his uncle Bernard, the former Ryder Cup captain, was unable to do in 1970.
"I'm delighted to still be in red numbers to be honest," Gallacher said. "It was a bit tricky, the wind is a bit up and the greens are firming up.
"It's a very strategic course. I think everybody back home knows how to play it, it's just a case of trying to do it that's the hard part. Generally I would say if I missed a green or anything like that, you have to be happy with bogey."
Former Open champion Louis Oosthuizen, who lost a play-off to Watson here 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.
Three-time Masters champion Phil Mickelson was heading for a first missed cut since 1997 after a triple-bogey on the 12th left him seven over par, but playing partner Justin Rose was one under for his round and three over for the tournament.
The top 50 players and those tied for 50th will make the cut, along with anyone within 10 shots of the lead.
Watson chipped to four feet for another birdie on the par-five 15th and when his tee shot on the next perfectly used the contours of the green to finish a similar distance from the hole, he calmly converted for a fifth birdie in a row.
At eight under par he enjoyed a four-shot lead from Bill Haas, with defending champion Adam Scott another two strokes behind following a bogey on the first.
Pre-tournament favourite Rory McIlroy, in the last group out, had parred the first but dropped a shot on the par-five second - usually a birdie opportunity - to lie level par.