Jordan Speth surged into contention with a sublime round of 63 at the AT&T Pebble Beach Pro-Am, including a daredevil shot off a cliff edge, as Ireland's Seamus Power blew his halfway lead.
Power's three-over 74 at Monterey Peninsula leaves him 13 under and two shots off the three-way tie for top spot ahead of Sunday's finale, with the 34-year-old dropping to seventh on the leaderboard after failing to back up his second-round 64.
Power is behind frontrunners Tom Hoge, Andrew Putnam and Beau Hossler (15 under) and also Patrick Cantlay, Joel Dahmen and Spieth, who are all on 14 under.
Spieth rocketed 30 places on Saturday with a nine-under round, his career-low at Pebble Beach, which was notable for a tense shot on the eighth hole on the edge of a sheer drop.
"That was by far the most nerve-racking shot I've ever hit in my life," Spieth said to caddie Michael Greller after his shot went just left of the green.
Hossler shot a bogey-free 65 to join Putnam and Hoge atop the leaderboard, while Jason Day and Denny McCarthy are joint eighth on 11 under and England's Matt Fitzpatrick is in a seven-way split for 10th on 10 under.
Hossler said: "Pebble can give and take so quickly, right? I was glad to be on the receiving end today.
"I hit it well, played really conservatively. I was fortunate to not have any misses to really get me in significant trouble. It was as fairly stress free as you can be around here."
Hoge posted his bogey-free round on Spyglass Hill Golf Club.
He said: "I don't know what it is, but I always seem to shoot better scores at Spyglass than I have at some of the others. I seem to play Spyglass a little bit better, so it was a good one for me today."
Putnam experienced a chaotic round on Pebble Beach Golf Links - starting on No 14, he settled down after posting a bogey and double-bogey in consecutive holes and would finish his round with seven birdies, including five in a row between holes four and eight.
"It was pretty ugly, that first nine," Putnam said. "It was a really bad start, a three-putt, kind of a stupid mistake. I then started hitting some good shots, and the putter started working pretty good on that front side."
Watch the AT&T Pebble Beach Pro-Am live on Sky Sports. Coverage of Sunday's final round begins at 3.30pm on Sky Sports Golf. The action is also on Main Event from 9.15pm.