Leonard, a two-time winner of this event, was tied with Paul Goydos at the end of the event's opening day -- one that produced low scoring at the LaCantera Resort course.
They had a one-shot lead over Jeff Maggert, Marc Leishman and Ted Purdy. Two-time U.S. Open champion Lee Janzen, current American Ryder Cup captain Corey Pavin and former world No. 1 David Duval were among the large group at 66.
Duval, whose career went into a decline after he captured the 2001 British Open, turned in his lowest 18-hole score of the year. He had failed to break 70 in any of his previous 14 rounds and he will be trying to make the 36-hole cut for just the third time in 11 events this season.
Defending champion Zach Johnson fired a 68. Alex Cejka, who blew a fourth-round lead last Sunday at the Players Championship, opened with a 73.
Goydos, who lost the 2008 Players Championship to Sergio Garcia in a playoff, posted his score in the morning and it appeared it would hold up for the outright lead.
Leonard, however, played a bogey-free round and got to within one of the lead with a stretch of three birdies in four holes beginning at the 13th.
He pulled his second shot at the par-4 18th well wide of the green, but pitched the ball in the hole to move into the lead at the end of a round for the first time this year. His best finish this season has been a tie for fifth.