MIAMI (AFP) - Defending champion Paul Casey fired a five-under par 66 to grab a share of the early clubhouse lead in Friday's (March 22) second round of the PGA Valspar Championship alongside American Austin Cook.

Britain's Casey and Cook each stood on six-under 136 after 36 holes at the Innisbrook Resort Copperhead course in Palm Harbor, Florida.

Luke Donald, Casey's English compatriot, was on the course at six-under overall with eight holes remaining.

Casey, who edged Tiger Woods and Patrick Reed by a stroke last year for the crown, began Friday on the back nine and promptly birdied three of his first four holes, sinking a 10-foot putt at 10 and landing his third shot inches from the cup before a tap-in at the par-5 11th.

Casey scored on the other par-5 holes as well, sinking a three-foot birdie putt at 14, a six-footer at the first before holing a 27-footer for eagle at the fifth.

But Casey's lone bogey came on his closing ninth hole, finding bunkers with his first two shots and missing a six-footer for par.

Cook opened with a birdie from seven feet, added a tap-in birdie at the par-4 third and then ran off three birdies in a row with 12-foot putts at the ninth and par-5 11th around one half as long to begin the back nine.

His only bogey came at 12 after finding a greenside bunker.

South Korean Im Sung-jae and American Scott Stallings were in the clubhouse on 137 with world number one Dustin Johnson another stroke adrift.