Mickelson birdied six of the first eight holes, becoming just the fourth player in Masters history to record a front-nine 30.
The others: Johnny Miller in the third round in 1975, Greg Norman in the fourth round in 1988 and K.J. Choi in the second round in 2004.
"The front nine was awesome," Mickelson said. "It was really fun, and it gave me a chance on the back. That's what we want as players."
Asked whether he and Woods fed off each other, Mickelson replied, "I don't think we were really paying much attention to what the other was doing."
Woods birdied Nos. 13, 15 and 16 to match Mickelson at 10-under-par.
But he missed the 17th fairway to the left and had to approach with a running hook. Then he pitched to 10 feet and missed the putt for par.
Woods pushed his drive on No. 18 and tried to punch his approach from the pine needles just to the left of a tree. Oops. His ball struck the tree and pinballed to the 10th fairway.
Woods lofted a terrific approach to about 10 feet but could not convert on the par save.
"My number was 11," Woods said after the round. "If I could post 11 [under par], then I thought I'd be all right."
He had to settle for 8-under.
More pain for Perry
Kenny Perry thought the toughest moment of his career had already happened, at the 1996 PGA Championship at Valhalla in his native Kentucky. Perry joined the broadcast booth rather than hitting the range, and he lost in a playoff to Mark Brooks.
"I've got two to think about now," he said.
But Perry looked at the bright side: Now he knows he can win a major. And he loved the support he received from the galleries.
"I think I lost my hearing on a couple of holes," he said.
Dustin Johnson joined Dan Pohl as the only players in Masters history to post back-to-back eagles, accomplishing the feat on the 13th and 14th holes. Johnson was 6-over before making the eagles. Pohl did it in 1982.