Tiger Woods' sumptuous summer continued with an opening six-under-par 66 in the United States PGA championship in Louisville, Kentucky yesterday.

But this time the world number one, chasing a third successive Major victory after his runaway triumphs in the US Open and Open, had company at the top of the leaderboard.

Little-known American Scott Dunlap, still to win a single US Tour title, matched Woods's effort to give everyone in the 150-field hope that this need not be another one-man show.

And Ulsterman Darren Clarke was only two behind after a round containing six birdies, but also bogeys on the ninth and 16th.

The huge crowds that were following Woods and, of course, playing partners Jack Nicklaus and Masters champion Vijay Singh saw the defending champion grab four successive birdies from the seventh and then another just two holes later.

That brought him one behind 37-year-old Dunlap the world number 67 and after shaving the hole on the next few greens Woods, trying to emulate Ben Hogan's unique 1953 feat of winning three Majors in one season, saved par from 12 feet at the 17th and then almost holed for eagle.

Nicklaus and Singh were not pulled along in his slipstream, however. Nicklaus, deciding to complete the day after his 90-year-old mother died, and Singh both had five-over-par 77s.

Woods said: ''It was an honour to play with Jack. I knew his mind was kind of elsewhere, though. As for my start, I will take four straight 66s.''

Nicklaus added: ''I had a hard time getting focused, but I really enjoyed watching Tiger.

''That's the first time we've played together in competition and the focus he had and the control of what he is trying to do amazed me. I was privileged to watch.''

Dunlap, battling a cold all week, had earlier chipped in for eagle at the second, bogeyed the next, but charged into top spot with four birdies in the following seven holes and like Woods closed with a birdie.

He said afterwards: ''They always say 'beware the sick golfer, the sick athlete or whatever'. I've been waking up in the night coughing my head off.''