Scott fell from two off the lead after round one to a distant eight shots back by firing a three-over 73 on Friday, leaving him at one-over 141 for the tournament.
American Jim Furyk was on track for a record score before a few late stumbles left him with a 64, still good enough to fashion a one-shot lead at seven-under-par 133.
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Englishman Justin Rose (68) was second alone at six-under while Masters champion Bubba Watson (66) and fellow American Bo Van Pelt (68) shared third two off the pace.
Senden started the tournament with a poor 72 but was four shots better in round two, his 68 moving him into a tie for 16th but still seven away from Furyk.
Both Queenslanders refused to throw in the towel, claiming Furyk's round, which included nine birdies, proved a significant move could be made.
"I feel like I can come out aggressively tomorrow because I know I'm still capable of low scores," Scott said.
"Jim Furyk showed you can get a hot round going. If you stiff a wedge in on the first and get on the front foot, it's there and I know I can do that.
"It's easier when you are way back as you have nothing to lose.
"It's all a bonus so you may as well have a go. I'll be out to have a crack tomorrow."
Senden could have easily been a few shots better with crisper play on the two par fives and a bit of luck on the 18th, the only hole he bogeyed when his par putt dangled on the lip.
He also stayed positive post round.
"I think I'm playing well enough to go under par the next two rounds and work my way back towards the top," Senden said.
"I just need one low one to get back in it."
"For me, I will be looking to get after it tomorrow and move into the top 10 or top 5 and from where I am now I think that's a realistic goal.
"Then from there anything can happen."
Overnight leader Tiger Woods also fell down the board into a tie for 12th after matching Scott's 73 and needed a similar approach to Saturday's third round.
"I didn't play very good today. Didn't hit it very good, and definitely didn't putt well. So it was a struggle all day," Woods said.
World no. 1 Rory McIlroy scratched together a 68 to be four back and tied seventh, still projected to win the FedEx Cup and the $US10 million ($A9.63 million) bonus, something he's trying hard not to think about.
He, along with Brandt Snedeker (T10), Woods (T12), Phil Mickelson (T16) and Nick Watney (30th) hold their destiny in their own hands knowing a win also brings the season long FedEx Cup title.
"First and foremost, I just have to try to think of my standing in this golf tournament, McIlroy said.
"Every now and then, of course (I think about the 10 million). I think it's natural.
"There is so much emphasis on it and everything. But first and foremost you've really got to concentrate on trying to stay in the moment and just think about this tournament.
"I'm only four shots back so I've still got a good chance going into the weekend."
