The 32-year-old Canadian fired an eight-under par 63 to stand on 19-under 194 after 54 holes at TPC Craig Ranch in McKinney, Texas.
"I'm swinging the golf club really good right now," Pendrith said. "I'm trusting my game, chipping it really well and putting it good. Just go out there and do the same as I've been doing and try not to worry about the other guys."
The bogey-free day, Pendrith's second-lowest PGA round, was good enough to seize the top spot over American Jake Knapp, who sank a 16-foot birdie putt at the par-5 18th hole for a bogey-free 67 to stand on 195.
It was the day's longest made putt for the 56th-ranked PGA rookie, who won his first tour title at the Mexico Open in February.
England's Matt Wallace and American Ben Kohles shared third on 196 with Sweden's Alex Noren and American Kelly Kraft sharing fifth on 198.
Pendrith seeks his first PGA Tour title with his best finish so far a runner-up spot at Detroit in 2022.
"I've been in this position a few times and haven't gotten it done," Pendrith said. "I think I've learned I've just got to go out there and be aggressive and keep making birdies, especially on a course like this where it yields so many birdies.
"It'll be fun. I'm looking forward to it."
Pendrith's eagles at the par-5 fifth and par-4 sixth lifted him into the lead at 16-under. He chipped in from 27 feet at the fifth and then chipped in from 41 yards two shots later at six.
"It was nice to see those fall," Pendrith said. "The first one had a little bit of speed on the chip and hit the pin in the middle and went around the hole and dropped.
"The second one was a beautiful shot that rolled in like a putt, so nice to get off to a great start through six holes.
Knapp matched him for the lead with a tap-in birdie at the fifth, two-putting from just inside 63 feet, and Kohles grabbed a share of the lead with an eagle putt at the par-5 ninth from just inside 12 feet.
Pendrith, ranked 107th, then sank a six-foot birdie putt at the ninth to reclaim the solo lead at the turn.
A birdie putt from just inside five feet at the 12th and another from just inside 18 feet at 13 lifted Pendrith to a three-stroke lead at 19-under.
Knapp dropped his approach inches from the hole at the 14th and tapped in for birdie and Kohles closed with a three-foot birdie putt as both pulled within two shots of the lead before Knapp trimmed another at 18.
Wallace, a four-time European Tour winner, seeks his second PGA triumph after last year's Puntacana Championship.
English 16-year-old amateur Kris Kim, the youngest player to make a PGA cut since 2015, fired a 70 to stand on 205.
"I realized how good my short game is, how I can rely on it sometimes, especially days like today where I sucked at hitting irons," Kim said. "Made up for it with wedges."
