Paul McGinley, Steven O'Hara, Alex Quiroz, Darren Griff, Corey Harris, Gonzalo Fernandez-Castano, Ross Bain, Ariel Canete, Gwang-Soo Choi and Paul Broadhurst are one shot back at 7-under-par 65.
Casey started on the back nine and picked up his first birdie of the day at the par-4 12th. He then birdied the par-5 13th and added another birdie at the par-4 14th.
The Englishman capped off that run with a birdie at the par-3 15th to make it four in a row. Casey continued his fine play on the front nine with back-to-back birdies from the first.
Casey parred his next five holes before a birdie at the par-4 eighth lifted him to 7 under. The 27-year-old then birdied the par-5 ninth to secure a piece of first.
Edfors birdied his first hole and collected birdies at the seventh and the ninth to make the turn at 3 under. He then holed out for an eagle at the par-4 10th and ran off back-to-back birdies starting at the par-5 13th.
The Swede birdied the 16th and added a birdie at the par-4 17th to jump to minus-9. He bogeyed the par-4 18th, however, to fall back into a tie with Casey.
Plaphol played the back side first and tallied four birdies and a bogey over his first nine holes. He then collected five birdies on the front nine for his share of first.
Anderson had a pair of eagles to go along with four birdies to complete the logjam atop the leaderboard.
Thomas Bjorn, Dean Robertson, Terry Pilkadaris, Bryan Saltus, Frankie Minoza, Michael Jonzon, Joong Kyung Mo, Miguel Angel Martin, Sam Little and Keng-Chi Lin are knotted at 6-under-par 66.
Colin Montgomerie, who won this event when it was last played in 2002, collected six birdies and a bogey to finish in a group at 5-under-par 67.