Bubba Watson surged to the Masters lead with a spree of birdies on the back side as the 2012 champion at Augusta National pushed his second-round score to eight-under with two holes to play.
The American produced a masterful display on the back nine to grab the outright lead at seven-under-par and hold a three-shot advantage over Australia's John Senden.
Another four players, including defending champion Adam Scott, were tied for third at three-under on a congested leaderboard.
The Australian battled to a 72 to join Denmark's Thomas Bjorn (68), Swede Jonas Blixt (71) and American Jordan Spieth (70), the last pair being among the record 24 rookies in the field.
"It wasn't exactly what I was looking for," Scott said. "But given everything, I'm absolutely satisfied with that."
The unflappable Fred Couples, the 1992 champion, finished with a 71 to join Jimmy Walker (72) and Jim Furyk (68) at two-under after Phil Mickelson missed the cut at the Masters for the first time in 17 years after finishing at five-over.