USGA water Oakmont greens

With no players under par after 36 holes of the US Open, the United States Golf Association took the decision to water the greens at Oakmont on Friday night.

The greens on the second, third, fifth, sixth and 13th - the firmest on the course - were then watered again early Saturday morning.

Only four players have carded sub-par rounds this week, two on each day.

Paul Casey shot a 66 on Friday, an achievement so outstanding that players stopped putting on the practice green adjacent to the ninth hole to applaud him when he finished.

There was no sign of an early improvement in the scoring, however, as US Masters champion Zach Johnson was four over after six holes.

New Zealand's Michael Campbell, the 2005 champion, was three over after four holes.

Angel Cabrera leads the way at level par, one clear of Bubba Watson.