World number one Rory McIlroy has admitted that he made mistakes on the greens at TPC Boston as he carded a one-under 70 at the opening round of the Deutsche Back Championship.

The 26-year-old is making his first appearance since finishing in 17th place at last month's PGA Championship at Whistling Straits.

"I felt like I hit the ball very well. These greens are probably the fastest I have putted on in a while," McIlroy told reporters.

"I was hitting the ball a little bit too hard at times and under-reading them, I just need to adjust to that. I hit a lot of good putts that didn't go in, and that probably has to do with the speed."

McIlroy, who had 31 putts during his opening round, trails first-round leader Brendon de Jonge by five strokes.