Scott, McIlroy launch late charge at Masters
Bubba Watson of the US plays a shot out of a bunker on the second hole during the second round of the 78th Masters Golf Tournament at Augusta National Golf Club on April 11, 2014 in Augusta, Georgia - by Emmanuel Dunand
Watson, the 2012 Masters champion, topped the leaderboard at six under. He birdied the seventh but took his first bogey of the tournament at the ninth, then torched Amen Corner for birdies at the par-3 12th and par-5 13th and added another at 14 to move two shots clear.
South Korean K.J. Choi and Americans Kevin Stadler and Bill Haas shared second on four under with Denmark's Thomas Bjorn in the clubhouse on three under.
Scott, who became the first Australian to win the green jacket last year when he beat Angel Cabrera in a playoff, opened on 69 but went off Friday in the penultimate group.
McIlroy, a fan and oddsmakers favorite this week, was the last man off the tee after opening on 71, joined by US rising stars Jordan Spieth and Patrick Reed.
McIlroy has proven most popular with the patrons in the absence of world number one Tiger Woods, who underwent surgery to repair a pinched nerve last week and is sidelined indefinitely.
Scott could overtake Woods atop the rankings with a two-way share of third this week.
Stadler, the son of 1982 Masters winner Craig Stadler and part of the first father-son duo in the same tournament at Augusta National, birdied the second and fifth holes to make the turn on four under.
He is among a record 24 first-time players in this year's Masters trying to become the first rookie to win a green jacket since Fuzzy Zoeller in 1979.
South Korean star Choi, 43 and playing on the last year of an exemption for winning the 2011 Players Championship, opened with back-to-back birdies to also reach four under.
Haas, who fired a four-under 68 to lead the field of 97 after 18 holes, opened with a bogey but answered with a birdie at the second hole.
The leaderboard looked similar to one from 30 years ago, when a Watson, Stadler and Haas were prominently featured. But those were current player dads Jay Haas and Craig Stadler plus legend Tom Watson.
Clubhouse lead for Bjorn
Bjorn birdied four of the last five holes to seize the clubhouse lead at three-under 144 after a second-round 68.
The 43-year-old Dane, ranked 29th, fired a 73 Thursday but moved up with a roller-coaster day, opening with back-to-back birdies before sizzling at the finish as well on a day with eight birdies and four bogeys.
Australia's Marc Leishman opened with three birdies to briefly take the lead.
But Leishman, who only qualified for the Masters based on his major career-best fourth-place showing last year at Augusta National, fizzled as quickly as he flashed, taking bogeys at the fourth, fifth and seventh holes to fall back.
Also rising and falling was 2010 British Open champion Louis Oosthuizen. The South African, who lost to Watson in a 2012 Masters playoff, made bogeys at the fourth and seventh holes and a birdie at the eighth. He eagled the par-5 13th but found the water of Rae's Creek and took an 8 at the par-5 15th.
American Kevin Streelman, the first man of the day to tee off, fired a 71 to stand on 143, good enough to stand in the top 10 as the last group departed.
"I really tried to focus on where to leave myself and where to not leave myself as well and just played really smart and putted well," Streelman said. "Drove it great and hit it where I needed to on the greens, gave myself some looks and made a few putts."
The low 50 and ties and anyone within 10 strokes of the lead will make the cut.
Among those players with concern about reaching the weekend after poor starts are three reigning major champions -- British Open champion Phil Mickelson (76), US Open champion Justin Rose (76) and 2013 PGA Championship winner Jason Dufner (80).
Also seeking a turnaround Friday are Ernie Els (75), Jason Day (75), 2013 Masters runner-up Angel Cabrera (78) and England's Luke Donald (79).