By Julian Linden
AUGUSTA, Georgia (Reuters) - Bubba Watson rolled in five birdies in a row to hold the outright lead late in the second round of the 78th Masters on Friday and surge into contention for a second green jacket in three years.
While most of the world's best golfers struggled to make par in brutally tough conditions at Augusta National, Watson produced a masterful display to grab the clubhouse lead at seven-under 137.
That left him with a three-shot lead over Australia's John Senden and a four-shot advantage over four players - Australia's defending champion Adam Scott and Denmark's Thomas Bjorn and Sweden's Jonas Blixt and American Jordan Spieth, who are among the record 24 rookies in the field.
Scott dropped three shots on his front nine to slip seven shots off the pace but picked up successive birdies at Amen Corner and another at the 15th to move into a tie for third with two holes to play.
Fred Couples, the 1992 champion, finished with a 71 to join Jimmy Walker at minus-two while three-time winner Phil Mickelson was in serious danger of missing the cut for the first time in 17 years after finishing the day at five-over.
Watson, who won the championship in an epic playoff two years ago, followed up his opening 69 with a sparking four-under-par 68, matching the best score of the championship.
The maverick left-hander made his first bogey of the tournament at the ninth hole and also dropped a shot at the last when he missed a short putt but reeled off five successive birdies from the 12th to seize control of the first major of the year.
"It's not science here," Watson said. "All I'm trying to do is just hit the greens, that means my tee shots are good and two putts, maybe throw in a birdie here or there.
"That's really all I was doing and that's what I've done the last two days and it's worked out so far."
Senden came into the first major of the year in good form after winning last month's Tampa Bay Classic. He was two-over after four holes but stormed up the leaderboard with six birdies in his next 11 holes for a 68.
With the wind gusting across the course and making the notoriously fast greens even more difficult to read, only a handful of players were able to make up any ground as the traditional roars around the Georgian pines were replaced by groans and sighs.
Bjorn, playing in the morning when conditions were less tormenting, birdied four of his last five holes while Blixt picked up two late birdies to consolidate his place after a double-bogey at the 11th, the opening leg of Amen Corner.
"It's a tricky golf course...if you're not quite on, it becomes extremely difficult out here," Bjorn said. "So, I just tried to do the right things and I executed it well."
Spieth, one of the leaders of golf's new generation, eagled the 15th to move into a four-way tie for third while many of his more experienced rivals slipped up.
TUMBLED DOWN LEADERBOARD
South Africa's Louis Oosthuizen, tied for second with Watson and Scott overnight, briefly grabbed a share of the lead when he eagled the par-five 13th after hitting his approach to eight feet from the flagstick.
But he quickly tumbled down the leaderboard when he made a triple-bogey eight at the 15th, then dropped another shot at the last to finish at level par.
"On this type of golf course, you know that can happen. You just need to focus and get on with it," said Oosthuizen, who was beaten by Watson in a playoff for the 2012 title.
"It's more disappointing on Sunday when something like that happens. At the moment, I'm in a good position for the tournament."
Last year's runner-up, Angel Cabrera missed the cut after finishing at eight-over while Mickelson was left facing an anxious wait to see if he would extend his record of making every cut since 1997 after he took a triple bogey at the treacherous par-three 12th hole when he found the bunker three times.
"I didn't play great. I didn't play bad," Mickelson said.
"I just had one bad hole there at 12. And I keep making these triples, they're tough to overcome."
Charl Schwartzel, the 2011 champion, Ernie Els, Sergio Garcia and Luke Donald were also just outside the projected cutline of four-over and sweating on some help to make the weekend.
Northern Ireland's Rory McIlroy, who blew a four shot lead on the final day of the 2011 Masters, was struggling at four-over par with three holes to play after making three double bogeys.
(Editing by Mark Lamport-Stokes and Gene Cherry)