Haas, who leads the money list and has eight top-10 finishes this year, shot a 6-under 65 in his first tournament round on the Glen Oaks Country Club course.
Dave Eichelberger, the 1999 U.S. Senior Open winner at Des Moines Country Club, opened with a 66, and 2001 Glen Oaks winner Jim Thorpe was another stroke back along with 2002 champion Bob Gilder, Mark James and David Edwards.
Haas was 5 under through 11 holes, sticking three approach shots within 5 feet for easy birdies. His early luck ran out on No. 12 when he hooked his drive into the rough and bogeyed the hole. He fell into a tie with Eichelberger with another bogey on the 467-yard, par-4 17th that is considered one of the toughest on the Champions Tour before pulling ahead with the long birdie putt on 18.
That putt, which broke at least 5 feet, capped a stellar day on the greens for Haas. He putted just 27 times.
Eichelberger fell behind with a double bogey on the fourth hole, then played bogey-free the rest of the way. He eagled the par-5 ninth hole, chipped in from 40 feet on 17 and finished with a birdie.
James was 1 over through eight holes before four straight birdies put him in contention. He bogeyed 16, but capped his round with birdies on his final two holes.
Tom Purtzer, Tom Wargo, Tim Simpson and Keith Fergus shot 68s, and Tom Kite and Denis Watson, the Senior PGA Championship winner two weeks ago at Kiawah Island, S.C., topped a group at 69. Kite hit 16 greens in regulation, but bogeyed four holes.
Defending champion Gil Morgan shot a 72, while Hale Irwin opened with a 73.
The wind, which many worried would keep scores high, died down after reaching 21 mph early in the day. Still, only 23 of the 77 players broke par.