Day charged to the lead and was in position to knock out Guan - and everyone else at 4 over, including defending champ Bubba Watson - until he stood over a 12-foot putt at the 17th hole.
Jason Day takes slim lead in the Masters
Jason Day is out front midway through the Masters.
Fortunately for Guan Tianlang, the leader did not sink one last putt on Friday.
Guan, a 14-year-old from China, became the youngest player to make the cut in PGA Tour history, despite taking a one-stroke penalty on the 17th hole for slow play.
Apparently the first ruling of its kind in the Masters' 77-year history, it gave the eighth-grader no margin for error if he wanted to play on the weekend.
Day charged to the lead and was in position to knock out Guan - and everyone else at 4 over, including defending champ Bubba
Watson - when he stood over a 12-foot putt at the 17th hole. When the ball slid by the right side of the hole, Guan could breathe a little easier.
Then, when Day's approach at the 18th rolled back toward the front of the green, it was clear Guan would reach another milestone — two more rounds in the first major of the year. He already was the youngest player in Masters history.
Day, an Australian, shot a 4-under 68 that gave him a 6-under 138 total, good enough for a one-stroke lead over Fred Couples and first-round co-leader Marc Leishman.
Tiger Woods had a share of the top spot until a tough finish knocked him back. He struck the stick at No 15, sending the ball careening back into the water. Only a brilliant little pitch on the do-over allowed him to save bogey at a hole where he should have had a good chance for a birdie. Then, on 18, Woods misjudged the distance just a bit on the approach, wound up on the back tier of the green and three-putted for another bogey.
He finished at 71 and three shots back at 141, a score that easily could have been two or three shots lower.
"I really played well," Woods said. "The score is not indicative of quite how well I played."
Everyone within 10 shots of the lead will be back for the final two rounds.
That includes a youngster who's on quite a field trip.
Guan just needs to speed things up a bit.
Fred Ridley, the club's competition committee chairman, said Guan's threesome was first warned for being too far behind the group ahead of them at the 10th hole. The teenager went on the clock two holes later — an official imposes a 40-second time limit to play a stroke — and gave Guan his first warning at No 13.
"In keeping with the applicable rules, he was penalized following his second shot on the 17th hole when he again exceeded the 40-second time limit by a considerable margin," Ridley said in a statement.
That turned what would have been a par into a bogey. Guan finished at 75 and 148 overall.
"I respect the decision," Guan said. "This is what they can do."
The last player to be penalised for slow play at a major was Gregory Bourdy at the 2010 PGA Championship at Whistling Straits. No one could find a record of anyone getting penalised in such a way at Augusta National.
"I know the rules pretty good," Guan said. "But I think my routine was pretty good, too. Just the wind changed. The weather, it was not a good day."
A rainy morning turned into a sunny, blustery afternoon, which sent scores much higher than they were in the opening round. Guan said it took him longer to judge distances and pick clubs because of the wind.
Leishman, a 29-year-old Australian with only one PGA Tour victory, kept up his solid play in the tough conditions, while others skidded down the board.
They included Sergio Garcia, who was tied with Leishman at the end of the first round after both shot 6-under 66. The Spaniard soared to a 76 that knocked him back, but not out. He was four strokes off the lead.
Dustin Johnson surged to 7 under and the top spot on the board, before a dismal finish ruined his day. He laid up at the par-5 15th hole, then dunked his third shot in the water, leading to a double-bogey. He bogeyed the 17th and took another double-bogey at the final hole to finish with 76.
Instead of leading, he was five shots back at 1-under 143.
Some former champions fared better.
Couples, playing in his favorite tournament at age 53, birdied the final hole for a 71. Angel Cabrera birdied five of the last six holes, signed for a 69 and was another shot back at 140.
"It's a hard course out there," Couples said. "I felt very good about what I shot. I had a couple of little hiccups out there and did some other good things to shoot my score. But the golf course is winning today."
Cabrera actually posted a better score in the tougher conditions than he did Thursday, when he shot 71. He was joined at 4 under by Jim Furyk (71) and Brandt Snedeker (70).
"For me, Augusta is never easy," said Cabrera, the 2009 Masters champion. "Never, ever easy. The big difference was that on the back nine, I was hitting very well off the tee, leaving my second shots close, and I was able to make some birdies."