England's Paul Casey was two shots off the pace alongside US Open champion Brooks Koepka, Webb Simpson and Daniel Berger, with Spieth's score matched by US PGA winner Justin Thomas and Spain's Jon Rahm.

Any of the 30 players in the season-ending event can theoretically win the massive pay day, but only the top five in the standings are assured of doing so by claiming the $1.53m first prize in Atlanta.

Open champion Spieth began the week with a 200-point lead over Thomas, with world number one Dustin Johnson, Marc Leishman and Rahm the other players in control of their own destiny.

The world number two was somewhat fortunate to be just one over par after five holes, but birdied the next three and picked up another shot on the 17th.

Playing partner Thomas carded six birdies and three bogeys to keep pace with his good friend, while Johnson recorded two birdies and 16 pars in a 69 matched by Olympic champion Justin Rose.

Stanley began the week 22nd in the standings and needs to win the Tour Championship and see other results go his way to claim the FedEx Cup title.

The 29-year-old carded seven birdies and one bogey in his 64 and told Sky Sports: "I'm very happy with it. It was nice to get off to something of a fast start and then make a few on the back nine.

"It's my first time here so we only played nine (holes) on Tuesday and nine on Wednesday and we were joking maybe that's not a bad thing. I love the golf course and I enjoyed the day."

Casey's chances of winning the FedEx Cup are slightly better after coming into the event in 10th place, the world number 16 finishing strongly with three birdies in his last four holes.

"I'm very happy," the 40-year-old said. "It's a golf course that doesn't yield a lot of birdies, it's tough and you have to strike the ball well and I did that today."