Tiger Woods launched a stunning back-nine charge to climb to within one shot of Australian Stuart Appleby's lead on day two of the US Open.
Woods, the 13-time major champion, ignored knee pain to fire 68, including a back nine of 30, to reach two under.
American Rocco Mediate and Swede Robert Karlsson were also two under with Lee Westwood and Spain's Miguel Angel Jimenez among those one under.
Luke Donald and Ernie Els were level par but Phil Mickelson slipped back.
Local favourite Mickelson, who has had four US Open runner-up finishes, carded a 75 alongside Woods to drop to four over on the par-71, 7,643-yard Torrey Pines South course near San Diego.
Jimenez, the PGA Championship winner at Wentworth last month, fired the round of the day, a 66, while Open champion Padraig Harrington shot 67 to better his opening score by 11 strokes and climb back into the mix at three over.
England's Oliver Wilson briefly shared the lead with Mediate before ending in a group on one over.
But despite Appleby's disciplined round of 70, capped by a monster birdie putt on the last, the day belonged to world number one Woods, who showed his tenacious competitive streak and laid down a definite statement of intent.
The 32-year-old, playing his first tournament for two months after knee surgery, began at the 10th and leaked two bogeys in his first three holes before making amends with an eagle at the long 13th.
Two further bogeys at 16 and 17 suggested he would not be edging closer to Jack Nicklaus's major haul at Torrey Pines, especially when he visibly grimaced and clutched his knee after hitting his second shot to the 1st green, his 10th.
Despite his pain, the ball landed 10ft away from the pin and Woods recovered to hole the putt for a birdie.
He went on to birdie three of the next four holes with a series of lengthy putts and added a closing birdie on the 9th to sign off.
"It wasn't an ideal start but you've just go to stay patient out there," said Woods, who won the second of his two US Open titles in 2002.
"I was just trying to get under par for the day but luckily I made some putts on that back nine and did a bit better than that."
Woods, who appeared to limp at times, said his knee was sore but added: "I'll be good to go tomorrow."
Westwood and Donald both carded 71s to maintain their push to become the first Briton since Tony Jacklin in 1970 to win the US Open.
"Any time you sign for level par in the US Open you can't complain," said Westwood.
And South Africa's Els, who won the US Open in 1994 and 1997, put himself in a good position to challenge for a first major title since the Open in 2002.
"Mentally I'm good, mentally I'm really up for it," said the world number four, who won the Honda Classic in March to end a lengthy barren spell.
"I've got no problem getting myself motivated. I had a couple of swing faults there on the back (nine) that I rectified and really made some good, aggressive swings coming in.
"I have played well in US Opens before so I kind of know what to do mentally and what to expect."
First round co-leaders Kevin Streelman and Justin Hicks tumbled down the leaderboard, ending on three over and six over respectively.
But they squeezed inside the cut, which came at seven over, eliminating the likes of Justin Rose, defending champion Angel Cabrera, Nick Dougherty, Colin Montgomerie and the British amateurs Gary Wolstenholme and Chris Devlin.
England's Ian Poulter was forced to withdraw with a wrist injury after finishing 15 holes on 14 over for the tournament.
