SAN FRANCISCO - One putt changed everything except the lead yesterday in the Presidents Cup.

The Americans were poised to seize control in the opening session of foursomes at Harding Park, already assured of the lead and on the verge of winning the final match for a two-point advantage.

Justin Leonard had a 3-foot birdie putt to win - a putt he first thought had been conceded - and was stunned when the putt caught the right edge of the cup and spun away.

The match was halved, and the Americans had to settle for a 3 1/2-2 1/2 advantage.

Tiger Woods and Steve Stricker were dominant from the start, playing bogey-free in the difficult alternate-shot format and teaming up for six birdies in a 6-and-4 victory over Geoff Ogilvy and 18-year-old Ryo Ishikawa.

Phil Mickelson and Anthony Kim closed with four straight birdies to give the Americans the first point of the matches with a 3-and-2 victory over Mike Weir and Tim Clark.

Leonard and Jim Furyk made a furious rally in the middle of the match and surged ahead of Retief Goosen and Y.E. Yang, 2 up with two holes to play.

Goosen holed a birdie putt on the 17th to send the match to the par-5 18th, and the South African missed the green to the right. Leonard hit a splendid fairway metal to the middle of the green, setting up what appeared to be a two-putt birdie.

Furyk lagged to 3 feet, the International team got up-and-down for birdie.

Americans Kenny Perry and Zach Johnson were in the tightest match of the session. Neither team led by one hole, and the match was all square with three remaining. The Americans birdied two straight holes to take the lead, then secured a point when Angel Cabrera's tee shot trickled into a bunker and left Camilo Villegas an impossible shot.

The International's Adam Scott and Ernie Els beat against mistake-prone Hunter Mahan and Sean O'Hair for a 2-and-1 victory. *