Mickelson shot 7-under-par 65 to finish one shot behind Steve Elkington after 18 holes of the BellSouth Classic near Atlanta.
'It's a tournament we're all trying to gear up for,' Mickelson said about the Masters. 'I'm just working hard on my game here. I think that's the best way to prepare for next week.'
Thomas Bjorn, Frank Nobilo, Dudley Hart, Ian Leggatt, Jesper Parnevik and John Rollins are all two back after shooting 66s.
Elkington, winless on the tour since the 1999 Genuity Championship, didnt post a par until his eighth hole at the TPC at Sugarloaf Thursday. He birdied the first two holes, but gave both shots back with a double-bogey-6 at the third. He then reeled off four straight birdies, and added another at the ninth.
The 1995 PGA champion tallied 10 birdies on the day to more than offset his lone hiccup.
Mickelson has won twice as many times on tour (20 to 10) as Elkington. However, the Aussie has one thing Lefty doesnt ' a major championship.
He's come under fire recently for his aggressive nature. But his play produced seven birdies and nary a bogey Thursday.
Bjorn is trying to do what hasnt been done on the PGA Tour since 1998. Over the past four seasons, Sergio Garcia, Jose Maria Olazabal and Parnevik have entered the Stateside winners circle, though they were PGA Tour members at the times of their victories. Others, such as Retief Goosen and Paul Lawrie, won major championships.
But not since Lee Westwood in 1998 has a full-time European Tour player won a regular PGA Tour event. The Englishman captured the Compaq Classic that season. Coincidentally, he did so the week prior to the Masters Tournament.
Thursday, Bjorn made six birdies and no bogeys in tying his career best round in the U.S. The Danes best tour finish came in a tie for second in Tiger Woods runaway victory in the 2000 British Open. He is best known, however, as the conqueror of the world's No. 1 player in last years Dubai Desert Classic.
While Bjorn is seeking his first PGA Tour victory, Nobilo and Hart are trying to regain entry into the winners circle.
Nobilo was on the fast track to stardom before his train derailed following his 1997 Greater Greensboro Chrysler Classic triumph.
The Kiwi slipped to 108th on the money list in 1998, and fell outside the top 150 in both 99 and 2000. Last year, he managed to avoid Q-School by once again ending the season No. 108 in earnings.
Harts descent hasnt been as drastic, though the same cant be said about his personal life.
The 33-year-old and his wife, Suzanne, had triplets in December. Since the additions, Hart has yet to record a top-25 finish. His last victory on tour came in the 2000 Honda Classic. He has, however, finished inside the top 60 on the money list each of the past six seasons.
This is the final tune-up before the seasons first major. Several top-ranked players are in the field. Defending champion Scott McCarron opened in 5-under 67. Goosen shot 68. Last weeks winner, Vijay Singh, bogeyed his final two hole to shoot 69. Colin Montgomerie, playing in his third consecutive tour event, also carded a 69.
Davis Love III has the roller-coaster round of the day. He went out in 42 and came home in 30 for an even-par 72.
Full-field scores from the BellSouth Classic