Jeff Maggert produced a run of birdies on the back nine to seize the lead at the US Masters in Augusta.
The little-known American shot a third-round 66 to emerge from the pack of players chasing Canadian Mike Weir to take a two-shot lead at the first Major of the year.
Maggert's run began at the 13th and he was five under par for the final six holes, including consecutive birdies at the last three.
The 39-year-old's best finish at this tournament was a tie for seventh in 1996 and he has never won a Major.
Weir, the leader after two rounds, stuttered his way around the course and he finished with a 75 to drop back into second place.
-5 J Maggert
-3 M Weir
-2 V Singh
-2 D Toms
-1 P Mickelson
-1 T Woods
-1 JM Olazabal
Also in contention is Tiger Woods, who came from 11 shots behind at the start of his third round to within four shots of winning his third consecutive Masters with another 66.
Woods, who had been perilously close to missing the cut earlier in the day, showed the form that has earned him his world number one status with a bogey-free round.
Two other former winners at Augusta, Fijian Vijay Singh and Spaniard Jose Maria Olazabal, are also in touch at two and one under respectively.
The 2001 PGA winner David Toms, playing with Maggert, is handily placed at two under while perennial contender Phil Mickelson stayed at one under.
But it was a sad day for Northern Ireland's Darren Clarke, whose faltering round was encapsulated by a nine at the par-five 13th which contributed to a round of 78.
Another British player, Paul Lawrie, dropped five shots in two holes but still finished with a respectable 73 and a one-over total of 217.