Lehman came into the third round five shots off the pace, but used the torrid performance to wrest sole possession of the lead at 17-under 193 on the Cochise Course at Desert Mountain Club.
Standings leader Lehman also put himself in position to win the Charles Schwab Cup for consecutive years -- a Champions Tour first -- if he can hang on for a victory Sunday.
Alone in second place at 16-under is Fred Couples, who drained two eagles en route to a third-round 62.
Second-round leader Jay Haas, coming off a course-record 60, stumbled to a 69, ending the day in third place at minus-15.
Defending champion and first-round leader Jay Don Blake (65) was is in fourth place at 10-under.