Jordan Spieth shot to the Houston Open lead on Saturday with a round to play, but a fairytale beckons for Austin Cook.
Spieth's five-under par 67 left him one stroke clear of a group of three players at the Golf Club of Houston, as he ominously builds form for next week's Masters.
The 21-year-old finished tied for second in his first Augusta appearance in 2014, but is poised to improve on that in '15 - after shooting six third-round birdies.
Among the challengers are Scott Piercy, Johnson Wagner and Cook.
Piercy has endured a tumultuous week - tying the course record in Humble, Texas in round one (63), before shooting 11 shots worse in his second round.
He moved from 18th back to a tie for second via a 66, which saw him go bogey free and shoot six birdies.
Wagner (66) joined Piercy in climbing into contention from outside the top 10, while Cook (70) held his spot after playing alongside Phil Mickelson (75).
Cook qualified for the PGA Tour event on Monday, and usually plies his trade on the inferior Web.com Tour and Adams Pro Tour.
On the latter, the 24-year-old has earned just $3,185 this season - but stands within reach of a stunning PGA Tour victory, which would also earn him a dream trip to The Masters.
Cook was three under through 14 holes, before a double-bogey at the par-five 15th threatened to derail his round - but he steadied with a birdie at the 17th.
He managed to outplay Mickelson, who dropped from a share of second to 18th after a three-over round.
Shawn Stefani (69) made it consecutive three-under rounds to be outright fifth on 12 under, two behind Spieth.
Englishmen Kelvin Day and Paul Casey (both 68) are level on 11 under, joining Americans Charles Howell III (69) and Russell Henley (68) in a tie for sixth.
Tied for 10th are Keegan Bradley (70) and Patrick Reed (67), the latter draining a hole-in-one on Saturday.
Reed, who did not require his putter twice in his opening round, once again bypassed the need for his short game, holing out from the tee on the par-three 16th.
Bradley and Reed are at 10 under, four shots behind Spieth.
Overnight leader Andrew Putnam (76) slipped to a tie for 18th.