After dropping back with bogeys on the 11th and 14th holes, Cantlay turned it around on the most difficult stretch at Harbour Town Golf Links with the late birdie run in strong wind swirling off Calibogue Sound.
Cantlay had a 9-under 133 total.
Streb also had a 67. He appeared to be in position to take the lead into the weekend when he birdied No. 8 -- his 17th hole of the day -- to reach 7 under.
But Cantlay's accurate irons and hot putter moved him back on top. The run started with a 13-foot birdie putt on 15. He caught Streb a hole later with a 10-footer. Cantlay stuck his tee shot on the par-3 17th within 8 feet for his go-ahead birdie, then rolled in a 21-footer on the par-4 18th.
"Obviously, that's a dream finish," Cantlay said. "I finally rolled in some putts and that was really nice to see going into the weekend."
Tour rookie Cameron Young went from his eye-popping debut of 63 on Thursday to a 73 in his second time around Harbour Town. Still, it was good enough to tie for third with Joel Dahmen, Cameron Tringale, Erik van Rooyen and Aaron Wise -- three shots behind Cantlay.
Dahmen, Tringale and van Rooyen had 67s to match Cantlay and Streb for low round of the day round. Wise shot a 68.
Among the six another stroke behind at 5 under were three-time major champion Jordan Spieth and past RBC winner Matt Kuchar. Spieth had a 68, and Kuchar shot 69. In all, it looks like a weekend shootout with 33 players within six shots of Cantlay.
Cantlay's steady and mindful approach to golf seems ready-made for Harbour Town. He's had two third place and a seventh place finish in four appearances here and made $878,178.50 -- and that's with missing the cut a year ago.
Cantlay expects more wind and doesn't expect to play much differently than he's done so far. "Just staying with my game plan and continue to leave the golf ball in the right spots, which is paramount around this place, I think is the key," he said.
Streb, who last won The RSM Classic in November 2020, has had a terrible experience at Harbour Town, missing the cut in four of his six career appearances. His best showing was a tie for 44th in 2015.
"Haven't played fantastic around this place, so getting it around in the wind was really good for me," he said.
Young shot a bogey-free 63 on Thursday in his course debut, the 24-year-old making Pete Dye's treacherous layout look like a roadside pitch-and-putt. Young kept up his stellar play with a birdie on his first hole, the 10th, to reach 9 under. Then he, like so many others before, felt Harbour Town's full fury.
Young had bogeys on the 14th, 15th and 18th holes, then a double bogey on the par-3 fourth. Still, the rookie is just another strong round from contention for his first tour victory.
"I feel like I'm hitting it really nicely and every chance I have to put myself in the fairway, even if it's 20 yards farther back, I think I'm going to take a lot of those chances," Young said.
The wind, with gusts of more than 20 mph much of the round, had a significant impact. After only seven holes played over par Thursday, 11 holes did Friday.
A couple of top draws won't be around for the weekend.
South Carolina native and world No. 9 Dustin Johnson went 71-72 to shoot 1 over and fall to 0-10 in PGA Tour events he's played in his home state.
Cameron Smith, who tied for third last week at Augusta National, also finished at 1 over to miss his first cut since the Sony Open in January. He shot 73-70.
Morgan Hoffmann, in his first PGA Tour event since October 2019 due to his muscular dystrophy, came up a shot short of the cut, too, also finishing at 1 over with rounds of 71 and 72.