PGA Tour news: Alex Noren and Tony Finau among first-round leaders in Houston

Noren mixed seven birdies with two bogeys at Memorial Park Golf Course, while Finau made six gains and dropped just one shot as they shared top spot with Aaron Wise and Tyson Alexander before darkness halted play.

"A little bit nervous coming into today," he said. "Didn't feel great in practice but found something and got the irons a lot better. So, yeah, good."

Finau's six birdies included a 35-footer at the ninth.

"It's kind of just icing on the cake on a day that's hard fought and well played," he said.

Wise, meanwhile, is looking for his first win since the 2017 Byron Nelson and only his second on the tour overall.

"I've just been in a weird place with my game where I'm obviously playing well enough to shoot good scores, but there's just a couple shots a round that are frustrating me," he said. "Maybe it's also just because it's late in the season and I played too much golf, and that's just kind of how golf gets."

Six players were in the clubhouse a shot back on 66: Canadians Mackenzie Hughes and Taylor Pendrith and Americans David Lipsky, Wyndham Clark, Max McGreevy and Keith Mitchell.

England's Justin Rose headed a group on 67.

Masters champion Scottie Scheffler, who could regain the world number one ranking he lost to Rory McIlroy last month with a victory, could do no better than an even par 70.