Rory McIlroy shot a one-under-par round of 69 on the opening day of the WGC Fed Ex St Jude Invitational in Memphis.
Irish Open champion Jon Rahm fired an eight-under 62 to storm into the lead after the opening round.
Dustin Johnson, who won last year’s St Jude Classic on the same course, also carded an opening-round 69.
The Spaniard sank a series of putts from at least 16 feet as he carded eight birdies for a bogey-free round in Memphis.
Equalling his career-low, Rahm gave himself a three-stroke lead ahead of five players tied for second.
Australian Cameron Smith joined Americans Patrick Cantlay and Bubba Watson and Japanese players Shugo Imahira and Hideki Matsuyama on five under, hitting rounds of 65.
Rahm, who won the Dubai Duty Free Irish Open earlier this month, said he had managed to adjust to the quicker greens than at last week’s Open at Royal Portrush.
He told the PGA Tour website: “I think it’s just imprinted in memory… It just felt good. Once you come into the tournament, and hit a few putts, for the most part it’s like you’re back here.
“To me, it’s always easier to adjust to quick greens than going to slow greens.”
Six players, including England’s Tyrell Hatton and Ian Poulter, went round in 66 to sit in joint seventh.