Jon Rahm fired an eight-under 62 to storm into the lead after the opening round of the WGC-FedEx St Jude Invitational, with Rory McIlroy some seven shots adrift of the Spaniard. 

The Spaniard sank a series of putts from at least 16 feet as he carded eight birdies for a bogey-free round in Memphis.

McIlroy, after missing the cut at the Open by one shot, carded four birdies in the last five holes to make up for a poor start to his round as he posted a 69. 

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 at Lahinch, 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.

Dustin Johnson, who won last year's St Jude Classic on the same course, carded an opening-round 69.