Justin Rose squandered a four-shot advantage, then birdied three of the last six holes to rebuild a two-stroke lead in Friday's second round of the 85th Masters.
The 40-year-old Englishman overcame a nightmare start to fire a level par 72 and stand on seven-under 137 after 36 holes at Augusta National.
Australian Marc Leishman shot 67 to stand second on 139 with Austrian Bernd Wiesberger, also seeking his first major title, third in the clubhouse on 140 after a 66 after both challenged for the lead.
Rose, twice a Masters runner-up, fired his lowest round in 59 tours of Augusta with a 65 on Thursday, defying firm and fast conditions to lead by four, matching the largest 18-hole Masters edge since 1941.
But reigning Olympic champion Rose began Friday with four bogeys in his first seven holes, briefly losing the lead to Leishman before a sparkling late fightback put him back on top.
Plenty of contenders were still on the course, led by Australian Cameron Smith, a 2020 runner-up who was 5-under after three birdies in the first four holes plus a birdie at the par-3 12th and an eagle at the par-5 13th.
Rose, whose only major title came at the 2013 US Open, stumbled badly in Friday's cool conditions, opening the door to rivals.
"With a little bit of overcast, it feels a little bit softer, a little more give," Wiesberger said.
Rose found trees to the right off the first tee on his way to an opening bogey for the second consecutive day.
At the 575-yard par-5 second, Rose chipped his third shot within three feet of the cup and rolled in the birdie putt.
Trouble returned, however, at the par-3 fourth and sixth and par-4 seventh holes.
On four, Rose was short of the green and his putt up a rise barely clung to the top edge. From there he putted to three feet and made bogey.
At six, Rose missed the upper tier of the green and his second shot rolled back to him. He sank an eight-footer to rescue bogey.
At seven, Rose sent his approach into a bunker and missed a 15-foot par putt, rescuing bogey from five feet.
Rose, ranked 41st, could only muster pars at eight through 12 on Friday after an eagle and three birdies a day before.
But at 13, Rose had a 35-foot eagle look and tapped-in for a birdie to share the lead with Leishman, then holed a 20-footer to birdie the par-4 14th and reclaim the lead alone.
Rose hit an 8-iron to 15 feet at the par-3 16th and holed the birdie putt to stand where he started the day at 7-under and closed with two pars. He's 9-under on the back nine for the first two rounds.
Leishman opened with three straight birdies and answered a bogey at the par-4 11th with birdies at the par-3 12th and par-5 13th and another at the par-5 15th to briefly seize the lead alone.
"Couldn't be more excited," Leishman said. "This is the position I wanted to be in. I'm excited for the next two days but there are a lot of good shots that have to be hit and putts to be made to put myself in good position on Sunday.
"Anyone who makes the cut has a chance."
World number 54 Wiesberger, without a top-10 finish in 24 major starts, had four birdies in the first five holes, added another at the par-5 eighth and rolled in a 30-foot birdie putt at the par-4 10th.
"In the first 10 holes, I holed a lot of putts and got a really good round started," Wiesberger said. "I've been playing really solid golf. I kept the mistakes off the card."
Wiesberger took bogey at 12 and birdied 15 then closed with three pars to complete his best of 22 Masters rounds.
"If I can keep my momentum going on the greens, I'm really looking forward to the weekend," Wiesberger said. "I was calm out there. It felt really nice. That's when I play my best."
- Finau, Thomas on fire -
Top-ranked defending champion Dustin Johnson was 1-over after four holes.
Second-ranked Justin Thomas, who can overtake Johnson for world number one with a victory, was on 4-under after 14 holes in a bogey-free round.
Also at 4-under with four to go was fellow American Tony Finau, who had three birdies and an eagle on the front nine.
Fighting to make the cut to the low 50 and ties were reigning US Open champion Bryson DeChambeau, four-time major winners Brooks Koepka and Rory McIlroy and England's Lee Westwood.