Americans Sam Burns and Sean O'Hair were the clubhouse leaders on Thursday in the first round of the RBC Canadian Open.

They were three shots ahead of the pack after 7-under 63 rounds. Burns had two eagles and O'Hair had one to lift them up to the top of the leaderboard.

"I think with all the rain we had early in the week the greens are still pretty receptive," said Burns after coming off the course at Hamilton Golf and Country Club. "It makes a big difference on par-5s when you have a long iron or a wood coming in there to be able to stop the ball pretty quick."

Two-time champion Rory McIlroy of Northern Ireland was in a group tied for fourth at 4-under par. McIlroy played with Canadians Nick Taylor and Taylor Pendrith and drew some of the biggest crowds of the morning.

McIlroy, third on the FedEx Cup rankings, said he was impressed with all the spectators who were at the 10th tee when the marquee trio teed off at 7:40 a.m.

"The Canadian fans came out to support them," said McIlroy. "One of the main reasons I love coming back here is because of that atmosphere that's created when we're out there to play, and playing with two Canadians today was, it was exactly what I expected."