The 59-year-old Haas, the winner of the major championship in 2006 and '08, had a bogey-free round. The 50-year-old Waldorf had six birdies and one bogey.
Haas has 16 Champions Tour victories after winning nine times on the PGA Tour. Waldorf is winless in 11 career starts on the 50-and-over tour after winning four times on the PGA Tour.
Australia's Peter Senior and Taiwan's Chien-Soon Lu each shot 68, and Tom Watson, a two-time Senior PGA champion, was another stroke back in a 12-player group that included Kenny Perry, Fred Funk, Rocco Mediate, Russ Cochran, Dan Forsman, Gil Morgan and Bill Glasson.
The temperature hovered in the low to mid-60s under overcast conditions. A light but steady rain fell three times in the afternoon, with each shower lasting less than 30 minutes.
Haas knows his way around Bellerive, finishing third in the 2004 U.S. Senior Open. He grew up in nearby Belleville, Ill., and has played about 30 rounds at Bellerive. His uncle, Bob Goalby, the 1968 Masters winner who stills lives in Belleville, followed him on the back nine holes.
Haas made his way around the course with a balky back that he said left him in "a little bit" of pain.
Waldorf finished ninth in the 1992 PGA Championship at Bellerive.
Murota had six birdies and a double-bogey. Skinner, a two-time winner on what is now the Web.com Tour, had six birdies and two bogeys and hit all 14 fairways in regulation.
Brian Fogt, the PGA director of instruction at Bellerive Country Club, led off the tournament by hitting the first tee shot. ... The field includes 34 international players representing an event-record 18 countries. France's Marc Farry, who earned a berth when David Frost withdrew, pushed the country total to the record. England leads with seven entrants, followed by Japan (4) and Australia (3). ... The PGA Championship will be held at Bellerive in 2018.