Smotherman won this event in Tijuana in 2018, when it was part of PGA Tour Latinoamerica.

On Thursday, he started on the back nine and put together birdie runs at holes 12 to 14 and 6 to 9, as well as a birdie on the par-4 3rd, describing his round as "super steady".

Erik van Rooyen of South Africa is tied for second with a 64 highlighted by an eagle at the par-4 15th. He collected six birdies and one bogey.

Argentina's Tano Goya was one of the last finishers and closed with his seventh birdie on 18 against no bogeys to join van Rooyen at a shot off the lead.

Tied for fourth at six-under are Mexico's Raul Pereda, Germany's Stephan Jaeger, Canada's Taylor Pendrith, and US players Eric Cole and World No.16 Tony Finau.

"I liked that it was really clean, I didn't make any big mistakes, any terrible swings off the tee to put myself in bad position," said Finau, who was a runner-up at this tournament last year.

"It was a solid way to start this golf tournament, no question."

Australia's Cameron Percy, Geoff Ogilvy and Aaron Baddeley sit in joint 65th, one-under after first-round 70s, while countryman Greg Chalmers lies a shot further back in a tie for 81st.

Harrison Endycott was one-over after 18 holes.

Smotherman's 63 was one stroke off his career low on the PGA Tour, where he has never won.

The 28-year-old said he felt momentum despite missing the cut last week with playing partner Harry Higgs at the Zurich Open in New Orleans.

"Harry and I played really good golf last week at the Zurich, we ended up missing the cut by two, but we were feeding off each other, hitting good shots," Smotherman said.

Defending champion and world No.1 Jon Rahm is tied with 16 others in 14th place at four-under.

He started on the back nine, where he carded two bogeys and two birdies, before a bogey-free front nine with four birdies.

"I'm happy with the score," Rahm said of his 67.

"Those first 13 holes we had virtually no wind, about as easy conditions as it can get. I wish I would have taken advantage of it more."

"I did make some good swings early on, I just couldn't quite get the number and judge some lies off the fairway."

Rahm, who has four wins in 10 starts in 2023, is seeking to become the first player to win five times in a season since Justin Thomas in 2016-17.