Mickelson also had a 67, one of his best rounds of the year in the LIV Golf League considering Trump National Bedminster has not yielded low scoring this week. He was one shot behind when he bogeyed the par-3 14th and failed to birdie the par-5 15th.

Queenslander Smith picked up birdies on the 15th, the par-3 16th and the par-5 18th. He is at nine-under 133, four shots clear of Mickelson and Dean Burmester, who had birdies on three of his last five holes for a 68.

The 2022 Open Champion is ranked No.8 in the world and No.2 in the LIV standings, just 15 points behind three-time winner Talor Gooch.

Smith won his first LIV title last month in London, while Mickelson, one of the chief recruits when the Saudi-funded league got going in 2022, is still looking for his first LIV title. His last success was the 2021 PGA Championship, when he was 50 and became golf's oldest major champion.

"It's been a couple years, and I would love getting back into that feeling of having a chance to win and having each shot bring that pressure about," Mickelson said.

Smith had a double bogey early in his round and did well not to drop more shots around the middle before he picked up momentum towards the end of the round.

"I probably had to lean on my short game a little bit more than I would wish, but that's where it kind of helps having a nicer short game," Smith said.

"When things aren't going your way and you can grind through a round and make some good pars. You never know when the driver and the irons are going to show up and you can start making birdies."

Fellow Australian Marc Leishman (69) is T8 at two under, with compatriots Matt Jones (70) five over and Jed Morgan (78) eight over.

Bryson DeChambeau, who shot 58 in the final round at Greenbrier to win, had a 73. He is at four-over 146, 13 shots behind, while PGA champion Brooks Koepka had a 76 to be six over.