Stuart Appleby, Rory Sabbatini, Stephen Ames, Trevor Immelman and 2003 British Open winner Ben Curtis are knotted with Mickelson atop the leaderboard.
Davis Love III, the 1997 winner, 1995 PGA Champion Steve Elkington, two-time U.S. Open winner Retief Goosen, Bernhard Langer, Jesper Parnevik, Heath Slocum, Greg Owen, Lee Westwood, Pat Perez, Ben Crane and John Rollins all posted 68s on Thursday.
One name not near the top of the leaderboard is that of the No. 1 player in the world.
Tiger Woods' quest for a third major championship in 2005 hit a snag on Thursday. He opened with a five-over-par 75 and is tied for 113th place.
'Every hole you could say there's something that I did wrong on the hole to not make birdie,' admitted Woods, who won this title in 1999 and 2000. 'That was frustrating.'
Woods began on the back nine Thursday and promptly bogeyed No. 10. He added bogeys at 14 and 18, then fell to four-over par for the championship with a bogey at the fourth.
Things got worse for the reigning Masters and British Open champion. Woods lipped out a seven-foot bogey putt at the seventh to move to plus-six. He rebounded at the eighth with a three-foot birdie putt, complete with a mock bow and tip of the hat after the putt fell.
'I've got to stay patient and build on it each and every day,' said Woods, who can become the first player in history to win three majors in one year twice. 'Patience helps and at least I'm still in it. There won't be too many guys under par by the end of the week and hopefully I can get myself there over the next three days.'
Mickelson drove into the rough on his third hole and had to chip back into the fairway. He made bogey at the hole, but reclaimed the lost stroke with a three-foot birdie putt at the fifth.
Things were interesting for Mickelson on the sixth. He hit a tree off the tee, then elected to play up the 17th fairway with his second shot. The No. 4 ranked player in the world hit a spectacular lob-wedge to five feet, but missed the par putt.
The lefthander picked up some steam around the turn with a pair of 35-foot birdie putts at the ninth and 10th holes. He was one-under par for the championship, but Mickelson kept it going with his putter.
At the 14th, Mickelson drained another long birdie putt, this time from 30 feet. He reached the green in two at the par-five closing hole and two-putted from 40 feet for a birdie and a share of the lead.
'There's a lot of good scores, don't get me wrong, and I'm very happy to be one of them,' said Mickelson, a three-time PGA Tour winner this year. 'It wasn't quite as stressful a round. I was able to keep the ball in play and hit a lot of greens in regulation and was able to make a few putts.'
Mickelson came within five strokes of winning the Grand Slam last season, but this year has not been close to that level of success. He took 10th in the Masters, but tied for 33rd at the U.S. Open and shared 60th at St. Andrews.
'I felt very confident last year going into the majors,' said Mickelson. 'I feel similarly this week in that the biggest difference is I feel like I know which way my misses are going to be with each club. I struggled a little bit this year missing it both ways in the majors, and the penalty for a miss is so great that I couldn't play effectively doing that.'
Appleby, who lost a playoff in the 2002 British Open, collected three birdies in his opening nine, the back side at Baltusrol. He bogeyed the first hole, but made back-to-back birdies from the rough off the tee at five and six.
The Australian was at four-under par, but ran into trouble with a bogey at the eighth. He went over the green with his approach and could not save par, dropping him into the logjam in first.
'The course has potential to get more difficult, but the greens generally are very round, so there's not many pins that can hide behind bunkers,' said Appleby. 'Everything is pretty visible from the fairway, unusual for a lot of the courses we play, even in normal tournaments.'
Sabbatini was one-over at the turn, but caught fire on the back nine. He sank an eight-footer for birdie at the 11th, then chipped in for a birdie at No. 12.
The South African closed the round with back-to-back birdies at the par-five closing holes. He ran home a 10-footer at the 650-yard 17th, then a 15-footer at the last.
'It's a course that really can give a lot, but it can take it away in a blink,' said Sabbatini. 'If you do have a birdie putt, really try to make some out there and capitalize on the situations because it kind of alleviates that stress on you.'
Ames was also one-over at the turn, but birdied three holes in a row from the 10th. He bogeyed 15 when he drove left of the fairway, but Ames, like Sabbatini, went birdie-birdie for his share of the lead.
Immelman, a 25-year-old South African, opened on the back side and broke into red figures quickly with a four-footer at No. 10. He dropped a shot at the 11th when his tee ball found the rough, but reclaimed the lost stroke with a 12-foot birdie putt at the par-three 12th.
He parred his next five holes, but made the turn at two-under par with a birdie at 18. Immelman drove it in the tall grass, but laid up short of the green at the par-five closing hole. He hit a wedge to 15 feet with his third to set up the birdie.
On the front side, Immelman played steady with seven consecutive pars. He collected his only birdie of the opening nine at the eighth, when his wedge stopped six feet from the hole.
'All in all, it was a pretty solid day for me,' said Immelman, who tied for fifth at the Masters and tied for 15th at the British Open. 'My putter really kept me in it, and I enjoyed it out there.'
Curtis recorded his first birdie at the fifth when his six-iron from a fairway bunker stopped four feet behind the hole. He parred the next eight holes around the turn.
At the 14th, Curtis knocked a nine-iron to 12 feet and rolled in the birdie putt. He parred 15, then got to minus-three with a spectacular tee ball at the par-three 16th. Curtis hit a three-iron to a foot at the 230-yard hole and tapped in the putt for his 67.
Defending champion Vijay Singh closed with back-to-back birdies at 17 and 18 to shoot even-par 70. He is tied for 28th.