Darren Clarke has had no difficulty finding somebody to thank after his brilliant opening 65 in the United States PGA Championship.

The Ulsterman, one ahead of Ernie Els and Justin Leonard entering Friday's second round, praised both Yorkshireman Billy Foster and American Stan Utley for the part they had played - and he hopes will continue to play as he seeks his first major title.

Foster is the caddie who carried Clarke's bag for seven years and is now back working with him after an 18-month break.

"In my infinite wisdom I thought I should try some other people, but it has been fantastic to have him back again," he said. "Billy's a decent player himself and sometimes I struggle to read greens. He has done a good job on that again."

Utley is the US Tour player who is also a renowned short-game expert and Clarke was advised to see him both by 50-year-old Jay Haas - himself round in 68 on Thursday - and by Dubliner Paul McGinley.

"I initially wanted to see him to try and hole some more putts and we worked very hard on that, but he is changed my chipping action quite a bit and it has definitely helped."

Haas joked: "I am a little hot about Darren spending Sunday, Monday and Tuesday with Stan. I will be giving him a little piece of my mind.

"He was very excited about what he was working on, but I guess I am a little surprised that if it was a complete revamp he picked it up so quickly."

Delighted though he was by his start - his best-ever in a major - Clarke kept insisting that it was only a start and it is where he is on Sunday evening that will determine whether it has been a great week or not.

And he knows this lunar landscape of a creation beside Lake Michigan is likely to be set up tougher after the unexpectedly low scoring on day one.

"I still think it is a par 77 really," he said.

In April last year Clarke led the Masters by three after an opening 66, but he fell all the way back to 28th, while at Royal Troon in 1997 he led by four on the second day, but ended up joint second behind Leonard.

The American is there again, but perhaps more worryingly for Clarke so are Els and Vijay Singh, both of whom have a chance to topple Tiger Woods as world number one this weekend - especially after Woods began with an error-strewn 75 in which he admitted he putted "atrociously".

Singh shot 67 and is in a group tied for fourth which also includes England's Luke Donald, taking yet another step towards a Ryder Cup debut after his victory in Sweden two weeks ago.

Three months ago Donald was not even eligible for the match, having resigned his European Tour membership because of the stipulation that he had to play 11 events on the circuit.

A few weeks later, however, he was back after being given the assurance that it applied only if he made the side - and that looks increasingly likely even if it is as a wild card.

Colin Montgomerie, who may need the other one, resumed on one over on Friday, but in an event which has not seen a European winner since Tommy Armour in 1930 Clarke and Donald are not the only two possibilities.

Padraig Harrington hit back from two over to four under to lie joint eighth, while fellow Dubliner Paul McGinley, second in Holland at the weekend and match-winning hero of The Belfry two years ago, returned a 69.

One further back is Londoner Brian Davis, like McGinley desperate to climb into a cup spot, and in his first major in America surprise Volvo PGA winner Scott Drummond opened with a 71.

Clarke's fellow Ulsterman Graeme McDowell had a 75 turned into a 77 because of a two-stroke penalty imposed because his caddie raked a bunker while he had still to escape from it.

Ian Poulter, ninth in the cup race, may not have done his cause much good with a 73, but in the publicity stakes he struck again.

After his Union Jack trousers of the Open last month he had the colours of the American flag this time. Right leg red and white stripes, left leg blue with white stars.

On that Clarke, who at the Masters in April unveiled pink and white pinstripe trousers with white turn-ups, commented: "He looks great, but you won't see me in them. There's quality and there's style.

"But I think Ian's fantastic - a breath of fresh air."