Richard Green of Australia, Welshman Garry Houston and Sweden's Henrik Stenson share second place at 5-under-par 67.
Ernie Els, who won last week's Dubai Desert Classic with an eagle on the 72nd hole, struggled on Thursday. He only managed a 1-over-par 73 and is part of a group tied for 81st place.
'I couldn't get anything going,' admitted the third-ranked golfer in the world. 'I just wasn't quite on and made a few mistakes. Nothing crazy, but it was frustrating. Now I need to get fired up and play better tomorrow.'
But Fulke, who played on the 2002 Ryder Cup team, had no problems on Thursday. He opened on the back nine and got his round going with three consecutive birdies from the 12th.
Fulke parred the 15th, then returned to his birdieing ways at the 16th. He made it two in a row at No. 17, but did not make the turn unscathed. Fulke dropped a shot at the par-5 closing hole to fall to 4 under par.
He reclaimed the lost stroke with a birdie at the par-5 first hole. Fulke added his final birdie at No. 7 which gave him the sole possession of the lead.
Fulke has gone down considerably since his Ryder Cup debut in 2002. He finished 88th on the Order of Merit in 2003 and 134th last year. Fulke thinks the reason for his decline is in part due to a new career path.
'There were lots of reasons. Really why I didn't play well after the Ryder Cup in 2002 is I just got very busy designing courses in Sweden,' said Fulke, who will be off the next eight weeks to complete his design obligations. 'The fact that I didn't play well after The Ryder Cup was self-inflicted because I was more passionate about designing than playing.'
Fulke better improve this season because his eligibility runs out at the end of the 2005 campaign.
'I've never worried about that before but I guess I do now,' said Fulke. 'It should concentrate the mind on playing again. I haven't done it the right way but this year I'm going to separate the two.'
Green was flawless on Thursday with five birdies and no bogeys. He has played well this year with a third-place finish in New Zealand, and the lefthander is hoping to improve on his 17th-place finish in last year's Order of Merit.
'I've been playing some good stuff,' Green said. 'Finishing third in New Zealand was good but I was a bit unlucky to run into the eventual winner, David Toms, in the first round of the WGC-Accenture Match Play.'
Houston was in one of the last groups to finish on Thursday and got within stroke of the lead with a birdie at the eighth. He had a chance to tie for the lead, but missed his birdie chance at No. 9.
Stenson climbed up the leaderboard with three birdies in a row from the 14th, his fifth hole of the round. He reached 5 under par with an eagle at the first and got into first with a birdie at No. 5. He dropped a shot at the eighth, but remained in second with a par at the last.
Stenson collected his second European Tour victory at last year's Heritage and kept the momentum going into this year. He has two top-10 finishes and is 20th on the money list.
'It's been a good time since I won The Heritage last September,' said Stenson. 'I am a little disappointed today as I left a few shots out there, but overall I am happy with the way things are going.'
Niclas Fasth, Anthony Kang, David Park and Stephen Scahill share fifth place at 4-under-par 68.
Defending champion Joakim Haeggman posted a 1-under 71 on Thursday and is tied for 38th.
Ian Woosnam, who was named Europe's Ryder Cup captain in 2006, was 4 under par until his final four holes. He tallied a birdie, a triple bogey and two bogeys to fall to even par. Woosnam is part of a logjam tied for 63rd.