Northern Ireland's Graeme McDowell shot a second round 68 at Pebble Beach to take the clubhouse lead halfway through the day at the 110th US Open Championship in California.
The recently crowned Celtic Manor Wales Open champion McDowell, from Portrush, carded a six-birdie, three-bogey round to reach three under par after 36 holes at Pebble Beach Golf Links and give himself a two stroke lead over Ernie Els, Ryo Ishikawa and Dustin Johnson with the late wave of starters just getting their second rounds under way.
McDowell, 30, had started the day on level par but reached the turn at two under thanks to an eventful four-birdie, two-bogey opening nine holes from the tenth tee. He added more birdies at the par four fourth and par-five sixth before closing with a three-putt bogey at the par four ninth hole.
"I got off to a sluggish, scrappy start but I made a great putt on 14 for birdie from 30 or 40 feet and that got my day going," McDowell said.
"I played lovely after that. There definitely are some chances out there but the second you get out of position this course can beat you up."
There was not better example of that than his bogey at the ninth, where his second shot had been delayed as players in the group ahead searched for a lost ball.
After a wait of more than ten minutes, McDowell finally played his second shot, getting his ball on the green but leaving himself a long birdie putt. He sent it off the green onto the collar and came back some four feet past the hole, still with work to do to with a downhill bogey putt.
"I hit a good drive there and the pin was front right and I said in practice that I was going to leave that (approach) shot on the front edge but in the cross wind today the front of that green wasn't very inviting and I went for the middle and hit it a little bit past the flag.
"I had a very treacherous two-putt which I three-putted."
McDowell said he would not let that disappointing end spoil his satisfaction at reaching halfway in the US Open Championship in such good shape.
"Generally, I'm very, very happy with three under par today," he said.
"It's great to be in position going into the weekend of a Major Championship. That's what I practice for and I've just to get through two more tough days on this golf course.
"So I'm just going to try and stay focused and calm about what I'm doing."
Two shots behind the Northern Irishman in the clubhouse were American Johnson, Japanese teenager Ishikawa and South African Els, who also shot a 68 to outscore marquee playing partners Lee Westwood and Tiger Woods by three and four shots respectively.
Johnson, who successfully defended his AT&T Pebble Beach Pro-Am title on the same course in February, carded a 70 while Ishikawa, 18, shot a level par 71.
Overnight co-leader Paul Casey of England recovered from a triple-bogey on his front nine, at the par five 14th, to card a 73 that kept him two strokes behind McDowell on level par after 36 holes.
World Number Nine Casey also bogeyed the ninth, his last.
Fellow co-leaders Brendon De Jonge of Zimbabwe and American Shaun Micheel had both moved briefly to the top of the leaderboard early in their second rounds. De Jonge carded a 73 to keep pace with Casey but Micheel shot a 77 that left him at four over, the same closing mark as World Number One Woods.
Westwood was a shot better than his playing partner at three over par on a much cooler, cloudier morning than the previous day on the Monterey Peninsula when the average score had been 75.288.
Based on the top 60 and ties being within ten shots of the lead, the projected cut was falling at seven over par, with McDowell's compatriot Rory McIlroy and Spain's Sergio Garcia among the players that looked to be at risk of a premature end to their US Open dreams.