Stenson, searching for his first PGA Tour win since the 2009 Players Championship, bogeyed his second hole but then produced four birdies to move to 20-under par at the second tournament of the four-event FedExCup playoffs.
American rookie sensation Jordan Spieth shot up the leaderboard to be one of five players three shots back of Stenson after firing a superb nine-under par 62 which ended with an eagle on the par-five 18th.
Overnight leader Sergio Garcia had played his first seven holes at two-over par with bogeys on the second, fourth and seventh holes, punctuated by a birdie on the par-four fifth.
Americans Steve Stricker, Roberto Castro and Jason Dufner were also on 17-under par while England's Ian Poulter moved to 16-under having reached the turn in 33, three-under par.
Rain had delayed the start of play by 90 minutes.