The start of play was delayed by almost two and a half hours due to fog, but Casey wasted little time in climbing up the leaderboard when the action did get under way.
Starting from the 10th, Casey birdied the 11th and 13th and, after dropping a shot on the 14th, hit back in style with four straight birdies to complete the back nine in 31.
That took the former Ryder Cup star to six under par for the tournament and alongside Garrett Willis at the top of the leaderboard, the American two under for 12 holes of his second round.
Casey is in need of a good finish as he currently lies 135th on the PGA Tour money list - with the top 125 at the end of the season securing their cards for next season - after struggling with a toe injury recently.
Tiger Woods has no such exemption worries, but the former world number one was also looking for an encouraging performance on his latest return to action.
Woods struggled to an opening 73, two over par, but covered his first nine holes in two under today to get back to level par and inside the projected cut mark.
Also starting from the 10th, Woods birdied the 11th from five feet but dropped a shot on the 13th after twice finding sand on the hole.
Woods then carded a hat-trick of birdies from the 14th to threaten a charge through the field, but dropped a shot on the 18th to be out in 34.