James Hahn moved into a one-shot lead as overnight leader Jason Kokrak crumbled at the AT&T Byron Nelson, but Jason Day was Saturday's top performer and surged up to joint third position.
Kokrak held a record five-stroke lead after 36 holes, but shot a two-over 72 that included a triple-bogey six on the par-three fifth to slip alongside Day and surrender his position at the top of the leaderboard to Hahn.
Hahn, who finished tied fifth at the TPC Four Seasons Resort in 2014, carded a flawless 64 to prime himself for just a third career victory on the PGA Tour, while a strong finish from Billy Horschel saw him birdie the last three holes to sit one back in second.
The leader's round was only outdone by former world number one Day. The Australian climbed 14 places with a seven-under 63 to sit just two shots adrift of the leader.
After a steady start to his round, Day strung together five birdies from the seventh to the 11th before dropping a shot at 14.
The Australian did not dwell on that and posted gains on the 16th and 17th, the latter with a monster 60-foot putt that put him in a tie for the lead until Hahn and Horschel moved clear.
"Everything was kind of clicking," Day told CBS Sports. "I was driving the ball wonderfully and gave myself the opportunity to hole a lot of putts out there.
"I feel a lot more like things are in balance now with regards to what happened earlier in the year, just kind of finding myself.
"This is a good step in the right direction, I just need to stay calm because there's one more round to go."
Masters champion Sergio Garcia was even par at the turn, but shot 29 on the back nine for a six-under 64 - his best round of the tournament - to climb 19 places for a three-way share of sixth.
After back-to-back 67s world number one Dustin Johnson started Saturday in third, but he went one over to slide all the way down to tied-19th.