Casey won three tournaments in four months in 2009, but only one since
Casey, on his way back from injury and looking for a second victory in 2011, played a flawless round featuring three birdies to move 11 under.
Woods, playing his first event since August, looked set to make a charge when he birdied the first two holes.
But a bogeyed third halted his momentum on the way to a 68.
However the former world number one, who has dropped out of the top 50 on the back of a run that saw him miss the cut at the US PGA in August, declared himself pleased with his progress as he carded consecutive sub-70 rounds for the first time since January.
"It's getting better," said Woods.
PAUL CASEY WINS SINCE 2009
- Jan '09 - Abu Dhabi
- Apr '09 - Houston Open
- May '09 - PGA Championship
- Jan '11 - Volvo Golf Champions
"I'm improving day by day, which is good. Tomorrow I need to improve a lot and make putts and post a really low one."