Australian Jason Day moved into the outright lead at the 77th Masters after a second round 68 left him six-under at Augusta.
The 2011 runner-up capitalised on Tiger Woods' misfortune after the world No.1's approach into 15 rebounded off the pin and into the surrounding pond, to take the initiative going into the weekend.
Day leads 1992 champion Fred Couples and co-overnight leader Marc Leishman who are both five-under, while another former champion Angel Cabrera shot 69 to move to within two of the lead alongside US pair Brandt Snedeker and Jim Furyk.
Amateur Tianlang Guan, the youngest player in Masters history, survived a shot-penalty for slow play to make the cut for the weekend but former major champions Graeme McDowell, Mike Weir, Webb Simpson and Y.E Yang are among those absent for the final two days.
English trio David Lynn, Lee Westwood and Justin Rose are all three shots off the lead, while Luke Donald is two shots back on one-under.
Sergio Garcia endured a customary second day collapse but remains in the hunt at two-under, level with world No.2 Rory McIlroy and German veteran Bernard Langer.
The day looked like belonging to Woods, who after three wins in 2013 and a return to the summit of the PGA rankings, remains the bookmakers favourite to claim a first major championship for five years.
But an inch perfect third shot on the par-five 15th went cruelly punished, as Woods' ball bounced off the pin and into the water. The American was up and down in two but his lead was lost.
A dropped shot at the last added to the 37 year old's woes but it is unlikely to diminish Woods' significant return to form.
Instead, Day, who finished second in two majors in 2011, took hold of the Masters going into the weekend and could have extended his lead had he not scuppered a birdie chance on 17.
The 2010 Byron Nelson Champion may lead going into Saturday but with three shots separating the top 13 alone, his lead remains perilous in one of the most open tournaments at Augusta for many a year.