Portugal Colonial - Colombia's Munoz leads Spieth by one at Byron Nelson

Munoz's 66 put him on 21-under 195 with Spieth on his tail after an eight-under par 64 for 196.

Chile's Joaquin Niemann carded his second straight 65 for solo third on 197 while American James Hahn produced a sparkling 61 for 198, tied with American Justin Thomas who shot a 64.

Colombia's Munoz started the day in a three-way tie for the lead alongside Ryan Palmer and Davis Skinns and on a day when birdies abounded at TPC Craig Ranch in suburban Dallas he wasted no time in separating himself.

Munoz rolled in a 39-foot birdie putt at the second to grab the solo lead on 16-under.

Hahn, Spieth and Niemann had joined Palmer on 15-under, one shot back, when Munoz quickly separated himself again, holing out for an eagle from a greenside bunker at the par-four sixth.

Munoz's shot from 57 feet flew straight at the hole, hit the pin and hopped in to give him a three-shot lead.

Munoz grabbed birdies at nine, 10, 12 and 14 -- where he fired out of a greenside bunker to three feet.

He bogeyed 16, and couldn't take advantage of the par-five 18th after a tee shot to the far right rough. But he had enough to keep his nose in front of local favorite Spieth.

The Texan is seeking a second victory in as many starts after his triumph at the Heritage in April.

He is also warming up for next week's PGA Championship in Oklahoma, where a win would give Spieth a career grand slam.

Spieth said he knew he'd need a low score to make progress in a tournament Munoz opened with a stellar 60 on Thursday.

He drained a 23-foot birdie at the third and an 11-footer at the fifth, then got up and down from a greenside bunker for birdie at the sixth.

- Sharpening up -

He strung together three birdies at eight, nine and 10 and almost drained a 22-foot eagle putt at 12. He followed a birdie at 14 with his only bogey of the day at 15, but closed it out with a birdie at the last.

Spieth said it was special to head into Sunday with a good chance to win a tournament that was the first one his father ever took him to as a child.

"It's really exciting, a lot of friends and family out, done a good job not putting too much pressure on myself," Spieth said. "I just wanted to get into contention and obviously see what needs to be sharpened for next week.

"But there's no better prep for a major than winning the week before."

Munoz also has ties to the area. He attended the University of North Texas and has a home in the Dallas area.

"Jordan is, of course, the golden boy here, so everyone's favorite. I'm good friends with him, so it's going to be a lot of fun tomorrow," he said.

Hahn, who won the most recent of his two PGA Tour titles at Quail Hollow in 2016, said "everything went right" in his 11-under effort that featured nine birdies and an eagle at the par-five 12th.

Palmer was in the mix on 20-under through 13 holes but finished with a double-bogey at 16 and bogey at the last to drop back. Skinns, a 40-year-old rookie from England, faded with a two-over 74.

A.S.Diogo--PC