Northern Ireland's Graeme McDowell shot a second round 68 to lead the 110th US Open Championship at the halfway stage in California as Masters Tournament champion Phil Mickelson stormed into contention.
The recently crowned Celtic Manor Wales Open champion from Portrush carded six birdies and three bogeys at Pebble Beach Golf Links on Friday to reach three under par after 36 holes and give himself a two stroke lead over fellow early starters Ernie Els, Ryo Ishikawa and Dustin Johnson.
Five-time US Open Championship runner-up Mickelson vaulted from four over par to one under after a thrilling round of 66.
England's Paul Casey and fellow overnight co-leader Brendon De Jonge of Zimbabwe are a further shot behind on level par after 73s, alongside American Jerry Kelly (70) and Alex Cejka (72) of Germany, while France's Gregory Havret is two over.
McDowell, 30, had started at 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."
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 Americans Mickelson and 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 carded a 70 while Ishikawa, 18, shot a level par 71 but the round of the day belonged to Mickelson, whose 66 featured five birdies in his first eight holes before adding a bogey and a birdie on his inward nine, having gone birdie-free in a first round plagued by putting troubles.
The World Number Two needed seven fewer putts than Thursday's 32 after making "a slight adjustment in the set-up".
"I made a lot of putts and don't feel like I left too many out there," Mickelson said. "I just got hot with the putter, was able to make some birdies on the birdie holes and just get through the tougher holes with some pars."
First round co-leader Casey recovered from a triple-bogey on his outward nine, at the par five 14th, to card a 73 that kept him two strokes behind McDowell on level par.
"It was a weird triple I made," world number nine Casey said. "I walked off thinking 'what happened there?'
"Incredibly frustrated with the score but I only hit one chunked pitch. The other seven shots were quite good."
There were mixed fortunes for Casey's fellow Englishmen in the world's top ten - number three Westwood, number six Luke Donald and eighth-ranked Ian Poulter.
Poulter dropped two strokes to finish at one over following a 73, Westwood (71) reached halfway at three over alongside compatriot Ross McGowan (73) and Germany's Martin Kaymer, and Donald slipped to four over after a 75, level with Ireland's Padraig Harrington (73).
Soren Kjeldsen ended the day one over par, and Rhys Davies of Wales did make it to the weekend on his US Open debut, his 70 leaving him at six over, while Northern Ireland's Gareth Maybin eagled the last for a 75 to sneak in at seven over.
World Number One Woods finished at four over but said he was satisfied with his position.
"I'm right there in the championship," the three-time US Open champion said. "I just need to make a few more birdies, a few more putts on the weekend and I'll be right there."
