* Stenson tightens grip on tournament with a 66
* Masters champion Scott in second after a 69
* Woods shoots a 71 after late collapse (Adds detail, quotes)
By Mark Lamport-Stokes
ATLANTA, Sept 20 (Reuters) - In-form Swede Henrik Stenson piled up four birdies in his first nine holes, then held steady after the turn to forge four shots clear in Friday's second round of the PGA Tour's season-ending Tour Championship.
With the FedExCup playoff title and its bonus jackpot of $10 million also on the line at East Lake Golf Club this week, Stenson tightened his grip on all those honours as he fired a four-under-par 66 on a glorious, sun-splashed day.
The Swede, ranked second in the FedExCup points standings coming into this week, offset a bogey at the 10th with a birdie at the 16th to post a 10-under total of 130 in the fourth and final playoff event.
"It might seem like a large lead, but four shots during two rounds is not that much," Stenson told reporters, having played with only 13 clubs in his bag after seeing that the face of his four-wood was caved in during his warm-up.
"I'm pretty cool about that. I'm just going to go out and try to do the best I can for the next two days, and hopefully that's good enough.
"I have won a lot of tournaments from a good position like this, and, I hope I can do it again," added the Swede, who has recorded five top-threes in his last seven starts, including victory at the Deutsche Bank Championship earlier this month
Stenson's playing partner, Masters champion Adam Scott, was alone in second, after carding a 69, with PGA Tour rookie sensation Jordan Spieth a further stroke back at five under, after a 67.
"I'm fairly pleased," Scott said after mixing three birdies with two bogeys. "I didn't play my best golf out there today. Not that I got in a lot of trouble but when you're out of position, it's really hard to have a good score around here.
"I scrambled well on a few holes, and I didn't get much to go down when I had opportunities. At least it's only one guy four in front, so four (shots back) is not so many at this point."
World number one and FedExCup points leader Tiger Woods, hunting his sixth victory of the season, made an early charge up the leaderboard as he rebounded from an opening 73 but spectacularly collapsed over his last five holes to card a 71.
That left him at four-over 144, a distant 14 strokes off the pace.
"I put everything I had into that start and didn't have much at the end," Woods, who had declined to speak to reporters the previous day after opening with a 73, said of his round.
"Just ran out of gas. I'm tired."
Once again, though, it was Stenson who commanded the spotlight as he continued his bid for a second PGA Tour victory this season.
One stroke in front of the chasing pack overnight, the Swede made a sizzling birdie-birdie start on another sun-drenched day at East Lake.
Stenson, whose ball-striking has been superb this week, rolled in an eight-footer at the par-four first, and holed out from a similar distance at the par-three second to move four shots clear, Scott having bogeyed there.
Though Australian Scott briefly trimmed the deficit with a birdie at the third, the Swede regained a four-stroke advantage when he drained a 28-footer at the par-four fourth.
Stenson picked up his fourth shot of the round at the par-five ninth, where he was just short of the green in two before chipping up to four feet, to maintain control of the fourth and final FedExCup playoff event.
Though Stenson bogeyed the 10th after finding a greenside bunker with his approach and missing a par putt from four feet, he rolled in a 22-foot birdie putt at the 16th then parred the last two holes to remain four strokes in front.
For the moment, Stenson has the FedExCup title in his control. At the start of the week, he and the other members of the top five in the standings - Woods, Scott, Zach Johnson and Matt Kuchar - knew they would automatically secure the playoff trophy with victory on Sunday.
U.S. Open champion Justin Rose of England (68) and Americans Dustin Johnson (68) and Billy Horschel (70) were tied for fourth at four under. (Editing by Frank Pingue)