South Africa's Charl Schwartzel jumped into contention at the Masters Tournament with a brilliant start to his second round.
Three over after three holes of his opening round, the 2011 champion was seven shots better off 18 holes later after an eagle on the second and birdie on the third.
At four under Schwartzel was three behind American Dustin Johnson, and experience of the course was looking more and more vital as 53 year old Fred Couples, the winner in 1992, also picked up a shot on the 13th to improve to four under.
Overnight joint-leader Sergio Garcia, however, was struggling to replicate his fine opening round.
A flawless first round 66 left the Spaniard level with Australian Marc Leishman overnight, but by the time Leishman began his second round after a morning punctuated by a swirling breeze and brief spell of rain, Garcia had dropped back to three under par and three off the lead.
After making pars on the first two holes, the 33 year old made a mess of the short par four third.
He did at least hole a putt from ten feet to drop only one shot, but also bogeyed the fourth to be out in 38 before doing well to salvage another bogey on the 11th.
After pulling his approach into the water left of the green he pitched to ten feet and holed a tricky downhill putt for bogey.
Garcia was not alone in struggling however, with Johnson suffering a dreaded shank on the par five second which sent his second shot all the way across the fairway and onto a spectator walkway crossing the adjacent third.
Johnson, third overnight after a 67, saved par there in between dropped shots at the first and third, and then birdied the fourth, ninth and tenth to join Leishman in the lead on six under.
England's David Lynn, playing only the third Major of his career and joint fourth overnight after an opening 68, had bogeyed the sixth to drop back to three under alongside compatriot Justin Rose, who had birdied the third.
Lee Westwood remained two under through three holes while Rory McIlroy, frustrated by more "silly mistakes" in his opening 72, recovered from two early bogeys in style with an eagle three on the eighth to get back to level par.
Meanwhile, Chinese schoolboy Guan Tian-lang, at 14 the youngest competitor in Masters history, was two over after 14 holes of his second round and three over for the tournament as he continued his remarkable performance.
With the cut extended to the top 50 plus any player within ten shots of the leader, the teenager still had a chance to be here for the weekend.
Garcia's disappointing day continued with a bogey on the par five 13th, and at two under par he was suddenly five off the lead held by Johnson.
The big-hitting American laid up on the 13th but pitched to seven feet and holed the birdie putt to become the first player to reach seven under par, which was good enough for a two shot lead when Leishman dropped his first shot of the day on the fourth.