Darren Clarke says his failure to putt well was the main reason for his opening five-over-par 75 in the US Open at Pinehurst.
"There's a little bit of frustration as has been the case pretty frequently this past while," Clarke told BBC Sport Northern Ireland's Stephen Watson.
"I'm hitting the ball OK. I hit a couple of poor shots but hit a lot of good ones. I drove the ball really well but I am not making the putts that you need to generate a score."
Clarke's round left him 10 strokes behind leader Martin Kaymer.