The trio is two shots ahead of a group of eight, which includes 2016 Masters champion Danny Willett and Ryder Cup duo Ross Fisher and Thomas Pieters.

Daniel Im is also part of that group after a bogey on the 11th halted a bright start by the American on a day of low scoring at Gardagolf in Brescia.

Lightning stopped play for an hour and 19 minutes midway through Thursday afternoon after Rock and Canter had both finished their rounds.

Rock was at one-over-par after three holes but carded nothing higher than a three on the next nine holes and finished with seven birdies and an eagle.

"I did well to bogey the second after two terrible tee shots, my provisional was in the water as well but got on a run after that with all threes and twos for nine holes," Rock said. "I don't think I've ever done that."

Canter looks on from the 13th tee during day one of the Italian Open at Gardagolf CC. PHOTO: Andrew Redington/Getty Images.

Rock won the first of his two European Tour titles at the 2011 Italian Open.

It was Willett's lowest round of the season as he looks to halt an alarming slide down the rankings.

He reached a career-high of ninth in the world after claiming his first major title at Augusta National in 2016 but has since plummeted to 462nd after struggling with injuries and a loss of form.

"It's been a while," Willett said after only his second round in the 60s this season.

"We played really well and got the ball in play a lot which you have to do around here."

Wade Ormsby is the best-placed Australian after the opening round and sits in a tie for 12th after shooting five-under 66.