Rory McIlroy shared the lead at the Memorial Tournament in Dublin, Ohio after he and American Chris Riley produced opening rounds of 66.
The Ulsterman was the only foreigner in the top 20 after the first day following his six-under-par performance, which saw him birdie three holes in a row from the sixth to find himself alongside Riley.
"I was really happy with the way I played," McIlroy told pgatour.com.
"I got off to a little bit of a scrappy start on my front nine, which was the back nine. I got it up and down a few times just to keep myself around one or two under par and then found a few birdies on the way in, which was the bulk of my birdies.
"I'm happy with 66, it's a great way to start the tournament."
The Ryder Cup star added: "This is one of my favourite weeks of the year and one of my favourite golf courses.
"I feel as if it really does set up well for me. I like these sort of golf courses, the likes of here and Akron and Quail Hollow, and I sort of feel as if I'm pretty comfortable on courses like that.
"I'm swinging well, I'm hitting it good, and I'm holing a few putts, so hopefully I can keep it going for the next three days."
A shot behind McIlroy and Riley were Chris DiMarco and Josh Teater after 67s while a group of nine on four under included Rickie Fowler and Stewart Cink.
Englishman Luke Donald's two-under saw him in a large group tied for 22nd. Justin Rose and Ernie Els were a further shot behind.