Jason Dufner shot a brilliant nine-under-par round of 63 to move to the top of the leaderboard at the RBC Canadian Open.

Heavy rain and lightning on Friday meant the whole field needed to complete their second rounds today and it was Dufner who fared the best as he moved on to 13 under.

It could have been even better for the 32-year-old, who has never won a PGA Tour title, but he bogeyed the 17th having previously racked up eight birdies and an eagle.

"I played very well, hit a lot of fairways, a lot of greens," Dufner said afterwards.

"It started raining at the end, conditions got a little tougher, but 63 is a pretty good score, and leading after two rounds is always great."

All of the players were able to complete their second rounds today, but the heavy rain set in once more forcing the postponement of the third round until Sunday.

Tour officials are hoping the weather will be more favourable then and allow 36 holes to be played.

Jerry Kelly and Scott Verplank are one behind Dufner on 12 under after both fired 67s while Australia's Nathan Green, who scored a 65 in the second round, and Peter Tomasulo of the US are on 11 under.

A group of six players are three off the pace, including Colombia's Camilo Villegas, South African Retief Goosen and Martin Laird of Scotland.

Calcavecchia, who began his second round on the back nine, was tied for 17th on eight under after his 65 today, which included nine consecutive birdies from the 12th hole to the second - a PGA Tour record.

That took the American to 10 under par but the gloss was taken off his achievement slightly by bogeys at the fourth and eighth.

Anthony Kim is usefully poised at nine under while England's Luke Donald, who finished tied fifth at the Open last weekend, comfortably made the cut on four under.

John Daly, however, was among those to miss out, the colourful American struggling to a level-par 72 today to finish at five over.