The two men expected to play bit parts in the $4 million Williams World Challenge didn't read the script in the first round of the year-ending tournament at Sherwood Country Club in California yesterday.

Mark O'Meara and Fred Couples - both playing on special invitations from the host - world number one Tiger Woods - each shot rounds of six-under-par 66 to share the overnight lead.

O'Meara, ranked 153rd in the world, and Couples, ranked 100th, upstaged a star-studded field that featured no other player above 32nd in the world rankings. However, when Couples - who had six birdies in his final 10 holes - rolled in a 40 footer on the last for par, it was sufficient to give him a share of the first round lead with playing partner O'Meara, and a two-stroke cushion over the chasing trio of Woods, Vijay Singh, the only player to have a bogey-free round, and Scott Verplank.

Ireland's two players, Padraig Harrington and Darren Clarke, both making their debuts in the tournament which is a financial perk to the game's top players with the last of the 18-man field guaranteed a $130,000 pay-day, remain very much within striking distance.

Harrington, sporting a new tight haircut, had a flying start with four birdies in the opening five holes before a double-bogey at the sixth stopped him in his tracks. He opened with a three-under-par 69 which included making a magnificent sand save on the last.

Clarke, despite turning in two-under, struggled on the greens and signed for a level-par 72.

O'Meara, who has struggled to regain his top form in the past couple of seasons, hit a superb 143-yard approach shot with a nine-iron to little more than two feet for birdie at the ninth to turn in 32 (four under) and then added further birdies at the 11th, 14th and 16th before dropping a shot at the short 17th.

Meanwhile, Woods, who initiated this tournament three years ago, but has yet to win, shot an opening 68 despite combating a tendency to pull his approach shots.

"I didn't strike the ball well," he said.