Denny McCarthy fired 10 birdies in a 10-under-par 60 on Thursday to grab a two-shot lead over Adam Scott and Keegan Bradley in the US PGA Tour Traveler's Championship in Cromwell, Connecticut.

McCarthy, chasing a first tour title, came astonishingly close to a 59, his approach from the fairway at his final hole, the par-four ninth, bouncing short of the green and finding the putting surface to roll past the edge of the cup.

"Saw it kick and couldn't see the rest," said McCarthy, who had opted to go with a seven-iron for the 170-yard shot.

"In the air I wasn't expecting it to be anywhere close to going in, but obviously it was exciting that it had a chance."

McCarthy's late-afternoon round capped a day of low scoring on the par-70 TPC River Highlands course, where 91 players shot in the 60s.

"My last two events have been US Open and Memorial, so coming into a place that doesn't quite beat you up as much, it's a little bit of a mindset change," said McCarthy, who fell to Viktor Hovland in a playoff at the Memorial earlier this month.

"It was nice to know from the start that it was gettable."

McCarthy "came out firing" at the 10th hole and was rewarded with birdies at his first four holes with another at the 15th.