Australian Robert Allenby led the Pennsylvania Classic before darkness set in at the Laurel Valley Golf Club. After 15 holes of his third round, Allenby is at 14-under-par - two shots better than American Rocco Mediate.
Eleven players have yet to complete their third round of the event, which has been disrupted by rain and fog. Kevin Sutherland has the clubhouse lead at 11-under 205.
Jay Haas and Cameron Beckman are at 10-under 206, tied with Zimbabwe's Nick Price and Aussie Steve Elkington, who were on the 17th hole when play was called off.
Sweden's Per-Ulrik Johansson is the leading European, tied for 21st place after a one-under-par third-round 71.
Allenby opened the third round with five birdies in seven holes but could not shake off Mediate, who birdied five of his first 11 to stay within two shots.
"Yeah, it was great," said Allenby, who thought the head-to-head battle was good for the crowd. "Obviously, I was making some and he was making some. He was holing some great putts and hitting some great shots."
Allenby also hit some great shots. Of his five early birdies in the third round, three were within three feet and two were no longer than a foot.
"When you feel that confident, you might as well just go for it because you know it's going to come off because you've got the confidence in yourself to do it," he said.
Allenby took a step back with a bogey at the par-five 11th but rolled in a 25-foot birdie putt at the 12th.
He missed birdie chances on what proved to be his final three holes as darkness overtook Laurel Valley.
"I was starting to fatigue and starting to get a little bit drained," said Allenby, who won the Nissan Open in a six-way play-off in February.