FedEx Cup golf: Dustin Johnson stays cool as Rory McIlroy stages recovery

He's a man on the verge of winning $10 million -- but Dustin Johnson says he feels "really relaxed."

The FedEx Cup leader had a share of the lead at the Tour Championship after Thursday's opening round in Atlanta and will claim the huge prize if he wins, although a top-five finish could well be sufficient.

Johnson, along with Japan's Hideki Matsuyama and fellow American Kevin Chappell, carded four-under-par 66 at East Lake, with Northern Irishman Rory McIlroy -- who must win to stand any chance of scooping the jackpot -- two shots further back.

McIlroy -- who recovered from a shaky start to hit seven birdies and keep himself firmly in the picture -- told UK broadcaster Sky Sports it would "be OK for the Ryder Cup next week playing like this."

The 27-year-old, who has been frustrated by erratic putting in recent weeks, said that aspect of his game remained a work a progress.

"I'm just happy that the score at the end of the day is under par," said the four-time major winner, who was tied for seventh in a group of four players including US rival Jordan Spieth.