After one round of the season finale, a familiar name is atop the leaderboard. Here's how things look at East Lake, where Henrik Stenson is off to a hot start as he looks to win the FedEx Cup for the second time in the last three years:
What it means: Stenson hasn't won yet this season, but he entered as one of five players in control of their own FedEx Cup destiny. His lone prior Tour Championship appearance came in 2013, when he left East Lake with both trophies, and he has already distanced himself from the pack. Playing for the first time as world No. 1, Jason Day sits six shots back after a 1-under 69.
Round of the day: Stenson got off to a quick start with birdies on each of his first three holes, but he hardly slowed down from there. He eagled the par-5 ninth to make the turn in 29, and he was briefly on pace to break 60 before closing the day's best round with five pars and a bogey on No. 17.
Best of the rest: Like Stenson, Casey hasn't won yet this season and actually hasn't won on the PGA Tour since 2009. But he is in contention after a round that included three birdies on each side against only a single bogey. Casey found 15 of 18 greens in regulation and closed with birdies on two of his final four holes.
Biggest disappointment: Louis Oosthuizen was a longshot to challenge for the FedEx Cup, but the South African's stay at East Lake was shorter than expected. Oosthuizen withdrew because of a hamstring injury after completing just 13 holes, reducing the field to 28 players and raising questions about his health for next month's Presidents Cup.
Main storyline heading into Friday: There is plenty of golf remaining, but all eyes are now on Stenson. The Swede has been known to heat up at this time of the year, having also won last year's season finale on the European Tour, and after a pair of runner-up finishes to open the playoffs he now appears poised to finish one place higher in the season's final event.
Shot of the day: Stenson had several accurate approaches, but it was his 4-wood approach on No. 9 that set up his lone eagle on the day. Stenson's shot from 288 yards ended up just 24 feet from the hole, and he rolled in the subsequent putt to make the turn in 6 under.
Quote of the day: "I was just trying to keep on doing what I was doing, and give myself as many chances as I could." - Stenson on his hot start