Forsman shot 8-under 64 for a one-shot lead after Friday's first round.
Haas, Jones and Wiebe all are 8-under 136, tied for second place.
"I like to think (my experience is) helping a lot," Forsman said. "I need to play one shot at a time (Sunday). It's exciting to be here."
Two-time defending champion Bernhard Langer (71) is locked at 5-under 139 in eighth place with Olin Browne (70), Bruce Lietzke (71), Russ Cochran (71) and Jay Don Blake (72).