Seamus Power birdied the final hole for a 5-under 65 and the St. Jude Classic lead Thursday, with Phil Mickelson, Steve Stricker and Brooks Koepka a stroke back on the crowded leaderboard.
Mickelson, who has six runner-up finishes at the US Open and could complete a career Grand Slam with a victory at Shinnecock Hills next week, said he kept his round together despite some late struggles at TPC Southwind in Memphis, Tennessee.
"I played here a year ago and it kind of suits my eye, so I kind of feel good going out", said Power, who tied for 27th here in 2017.
Power, who attended university in Tennessee, was unable to secure a US Open spot in sectional qualifying in Memphis earlier this week - earning only second-alternate status.
"Oh, it was a great start for me", Mickelson said.
Quote of the day: "I mean, there's nothing better than winning a golf tournament going into a major".
Meanwhile, defending US Open champion Brooks Koepka matched Mickelson's 66 on Thursday, saved by a putter that was nearly as hot as the Memphis weather.
US Open holder Koepka had been a doubtful starter for the defence of his title after being sidelined by a wrist injury for nearly four months earlier this year, but he has looked sharp in his last three starts after following a tie-for-11th at The Players Championship with a runner-up finish at Colonial. "We hit some pretty poor shots, we were kind of all over the place, but hope to figure this out for the rest of the week".
"I'm a good putter". Just need to continue to do what I do and obviously a three-peat would be fantastic.
World No.2 Dustin Johnson also started well with a 67 that included a chip-in birdie at the par-4 12th.
After his approach shot ended in a hazard but dry, Johnson removed his right shoe and sock, took his stance in the mud and choked down on his wedge, before knocking the ball into the hole. "I didn't play well at all, to be honest with you".
"Three-under's a solid score around here", he said.