Washington - Colombia's Sebastian Munoz torched the Country Club of Jackson for a nine-under par 63 on Saturday to grab a one-shot lead over friend and former college team-mate Carlos Ortiz at the PGA Tour's Sanderson Farms Championship.
Munoz, 26, had a 16-under par total of 200 and put himself in prime position to challenge Sunday for a first US tour title.
But he'll have to hold off Mexico's Ortiz, who had an eagle and five birdies in his seven-under 65 for 201.
South Korea's An Byeong-hun, who started the round with a two-shot cushion, tussled for the lead with Munoz and Ortiz for much of the afternoon.
Three straight birdies at 13, 14 and 15 moved him to 16-under but he slipped back with bogeys at 16 and 17 and signed for a two-under par 70 that left him alone in third on 202.
He was one stroke in front of Australian Cameron Percy, who posted a 68.
Munoz and Ortiz, once team-mates at the University of North Texas near Dallas, will duel in the final group on Sunday after playing together in the third round as the tournament finally worked its way back on schedule after a hefty weather delay on Thursday.
Munoz, who was five shots adrift through 36 holes, set the tone early with birdies at the first, second and third holes. He added birdies at the fifth and eighth - where he rolled in a 15-footer - to make the turn at 13-under.
"It was pretty comfortable," he said of playing alongside Ortiz, who is two years his senior.
"Good vibes from the beginning. he made birdies, I made birdies and we kept it going all the way.
"It was great when I started with three birdies in a row. I kind of flattened out a little and then Carlos came for me so we gave it a little extra run and it was fun," added Munoz, who took sole possession of the lead for good with a 14-foot birdie at the 17th.
Munoz, whose three prior wins as a pro have all come in Colombia - including the 2016 Colombia Championship on the Korn Ferry Tour, is coming off a tie for seventh at The Greenbrier last week.
"It made me feel like I'm close, I'm close here again," he said.
"Ready for another great day Sunday."
After two front-nine birdies, Ortiz did most of his damage on the back nine of the par-72 course, holing out from a bunker for a birdie at the 10th before draining an 18-foot eagle putt at 11.
He picked up one more birdie at the 15th, where he blasted out of a greenside bunker to nine feet and made the delicate putt.
Leading scores after Saturday's third round of the PGA Tour Sanderson Farms Championship at Jackson, Mississippi (par-72, USA unless noted):
200 - Sebastian Munoz (COL) 70-67-63
201 - Carlos Ortiz (MEX) 65-71-65
202 - An Byeong-Hun (KOR) 66-66-70
203 - Cameron Percy (AUS) 65-70-68
204 - Dominic Bozzelli 70-67-67, Im Sung-jae (KOR) 68-69-67, Harris English 65-71-68, J.T. Poston 64-70-70, George McNeill 67-67-70
206 - Zach Johnson 67-71-68, Robert Streb 65-72-69, Scottie Scheffler 68-66-72
207 - Cameron Tringale 70-68-69, Dylan Frittelli (RSA) 71-69-67, Fabian Gomez (ARG) 72-66-69, Charley Hoffman 73-64-70, Richy Werenski 69-68-70
208 - Zack Sucher 69-69-70, Kevin Streelman 72-67-69, Bronson Burgoon 69-69-70, Lanto Griffin 71-67-70, Brian Harman 71-69-68, Garrett Osborn 70-67-71, David Hearn (CAN) 68-73-67