Dustin Johnson, not unexpectedly, soon was alone at the top of the AT&T Pebble Beach Pro-Am leaderboard on Saturday, when entirely unexpectedly a relatively obscure interloper overtook him.

Ted Potter Jr flirted with a 59 at Monterey Peninsula Country Club, before bogeying his final two holes to settle for a nine-under par 62 and a share of the 54-hole lead with Johnson.

Jason Day, meanwhile, quietly played himself into contention. Day, who won the Farmers Insurance Open two weeks ago, shot a three-under par 69 at Pebble Beach Golf Links to get within two of the lead.

Potter, a left-hander whose lone US PGA Tour victory came at the Greenbrier Classic in 2012, had nine birdies and an eagle to momentarily take a two-stroke lead before his late stumble.

Johnson went out in four-under 32 at Pebble Beach and appeared headed for his third victory in the event before the back nine tripped him up and he settled for a two-under 70.

“Once we turned and came back into the wind from 11 to the house, the course definitely played pretty tough,” Johnson said. “But it was still out there. I still had a bunch of chances. I just hit a lot of good putts that didn’t go in and got out of position on a couple holes, which was the only time I made the bogeys, and it really was just from the second shots on those. I know where I can’t hit it and I hit it there anyway. But tomorrow hopefully will be a little bit sharper.”

Beau Hossler, who shared the 36-hole lead with Johnson, made four bogeys at Monterey Peninsula CC after playing the first two rounds bogey-free. He settled for a three-over 74 to fall into a tie for ninth.

Steve Stricker, who will turn 51 in two weeks, is three off the lead following a round of two-under 70 at Pebble Beach.

“I still feel like I’m capable of winning out here,” he said. “Obviously I’ve got to do a lot of good things to do it.”