Lehman shot a 5-under 67 and Baird a 4-under 68 for a 54-holde total of 17-under 199.
Vijay Singh, the defending champion and World No. 1, is one of four players at 14-under 202 after a third-round 65.
Lehman, 45, struggled early as he dropped a stroke at the par-four second. The 1996 British Open champion erased that mistake with an eagle at the fourth.
"It was a good day," said Lehman. "Briny played extremely well on the back nine and I played extremely well on the front," Lehman said. "I think no matter what they do with the pins, it's still going to be a birdie-fest."