The Canadian birdied all four of the par fives in South Carolina, dropping only one stroke en route to shooting a five-under 67.

Six players are two shots behind, including Brooks Koepka, a two-time winner of the Professional Golfers' Association of America's (PGA) flagship event and a four-time major champion.

The American overcame a double-bogey opening hole - the 10th - to shoot 69, boosted by three birdies in his closing six holes.

Compatriots Keegan Bradley - the PGA Championship winner in 2011 - and Aaron Wise are also on three under, along with Norway's Viktor Hovland, England's Sam Horsfield and Cam Davis from Australia.

Only those seven players to broke 70 - the fewest in the opening round of the PGA Championship since 2002.

Defending champion Collin Morikawa shot 70 and is in a group three shots back which also includes fellow American Phil Mickelson, five times a major winner.

Rory McIlroy, who won here in 2012 and earned a first PGA Tour victory since 2019 earlier this month, ran into trouble on the second half of the round, with four bogeys taking the Northern Irishman to three shots over par.

Dustin Johnson of the United States - the world number one - is a further shot back.

Jordan Spieth of the US, who would complete a career grand slam with victory this week, is one over, as is Japan's Masters champion Hideki Matsuyama.

The second men's major of the year, the PGA Championship is due to conclude on Sunday (May 23).