Australians Greg Chalmers and Robert Allenby sit two shots off the lead after the opening round of the US PGA Tour’s Canadian Open.

Americans Tim Petrovic and Michael Putnam posted six-under-par rounds to share a one-shot lead over compatriot Kyle Stanley and Canadian amateur Taylor Pendrith.

Chalmers and Allenby were among a big group of players in a tie for fifth after carding four-under rounds.

Pendrith, 23, birdied the final hole at Royal Montreal Golf Club after sinking a 29-foot birdie putt on the par-three 13th, while Petrovic posted three birdies on the trot from the second hole and added another on the seventh before eagling the par-five 12th.

Putnam, seeking his first PGA Tour crown, opened at the 10th tee and birdied 12 and 17, then picked up birdies at the second, third, fifth and eighth coming in.

Stanley also teed off on 10 and made five birdies in his first nine holes.

He gave back a stroke at the third, but birdied the sixth to finish the day one off the pace.

Jim Furyk, coming off a fourth-place finish at the British Open, and Spaniard Gonzalo Fernandez-Castano were in another big bunch on three-under.

Petrovic, who got into the field only after the withdrawal of Benjamin Alvarado, made the most of his opportunity.

“I really didn’t set my expectations high because I got in late,” he said.

“It wasn’t that I was playing conservative, I was just trying to hit fairways and greens just to see the golf course.”

Northern Ireland’s Graeme McDowell delivered the day’s highlight, holing his approach at the par-four 11th from 213 yards out for an eagle.

He was among a group on two-under 68.