Jason Day overcame an injury to his coach and caddy to be just one off the lead after the opening round of the Tour Championship.

Jason Day and Adam Scott have kept the dream of winning the lucrative FedEx Cup alive after solid starts to the US PGA Tour Championship at East Lake Golf Club.

Day is just one shot off the lead after shaking off a back injury, and the loss of his caddy and coach Col Swatton to a hip complaint, while Scott endured a late hiccup but sits just three off the pace.

Americans Chris Kirk and Billy Horschel, the last two winners in the playoffs and the current FedEx Cup leaders, continued their impressive form to share the lead at four-under 66.

Should they remain near the top of the leaderboard through four rounds it will be difficult for anyone else to claim the trophy.

Day and Americans Patrick Reed, Jim Furyk and Bubba Watson shared third after rounds of 67 while Scott was part of a tie for 11th with a 69.

For Day the round was impressive given he was forced to pull out of last week’s playoff event with a back strain and he lost caddy and coach Colin Swatton, the man who has carried his bag for every professional round of his career, to a hip joint injury seven holes into his round.

Day was even par at the time but with mental coach Jason Goldsmith taking over as caddy for the final 11 holes he was forced to concentrate harder and produced three birdies.

“The ultimate goal is to win the tournament and hopefully win the FedEx Cup,” Day, who must win and have other results fall his way to claim the $US10 million ($A10.82 million) bonus, said.

“I’ve been preparing for a long time, getting treatment on my back for two to four hours a day, and I’m very motivated to play well here.

“So the focus didn’t really go up as much because Col pulled out but just because there is so much at stake here.”

Scott held a share of the lead at one point after four straight back nine birdies but bogeyed his final two holes to fall back off the pace.

“Anything in the 60s you can’t be too disappointed with. It’s tough out there and I played all right,” Scott said.

“I just have to try to eliminate some mistakes going forward. I missed a couple of short putts but I am hitting it well so I need to stay patient knowing the birdies will come.”

John Senden has a lot of work to do to claw back into the tournament after a 72 left him tied for 23rd while Geoff Ogilvy had a day to forget, shooting 77 to be dead last in the 29-man field.